ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 25 Jul 2021 12:53:13 GMT2021-07-25T12:53:13Z50751- Quantum absorption refrigerator with trapped ionshttps://scholarbank.nus.edu.sg/handle/10635/174186Title: Quantum absorption refrigerator with trapped ions
Authors: Maslennikov, G; Ding, S; Hablützel, R; Gan, J; Roulet, A; Nimmrichter, S; Dai, J; Scarani, V; Matsukevich, D
Abstract: In recent years substantial efforts have been expended in extending thermodynamics to single quantum systems. Quantum effects have emerged as a resource that can improve the performance of heat machines. However in the fully quantum regime their implementation still remains a challenge. Here, we report an experimental realization of a quantum absorption refrigerator in a system of three trapped ions, with three of its normal modes of motion coupled by a trilinear Hamiltonian such that heat transfer between two modes refrigerates the third. We investigate the dynamics and steady-state properties of the refrigerator and compare its cooling capability when only thermal states are involved to the case when squeezing is employed as a quantum resource. We also study the performance of such a refrigerator in the single shot regime made possible by coherence and demonstrate cooling below both the steady-state energy and a benchmark set by classical thermodynamics. © 2019, The Author(s).
Tue, 01 Jan 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1741862019-01-01T00:00:00Z
- All the self-testings of the singlet for two binary measurementshttps://scholarbank.nus.edu.sg/handle/10635/175263Title: All the self-testings of the singlet for two binary measurements
Authors: Wang, Y; Wu, X; Scarani, V
Abstract: Self-testing refers to the possibility of characterizing uniquely (up to local isometries) the state and measurements contained in quantum devices, based only on the observed input-output statistics. Already in the basic case of the two-qubit singlet, self-testing is not unique: the two known criteria (the maximal violation of the CHSH inequality and the Mayers-Yao correlations) are not equivalent. It is unknown how many criteria there are. In this paper, we find the whole set of criteria for the ideal self-testing of a singlet with two measurements and two outcomes on each side; it coincides with all the extremal points of the quantum set that can be obtained by measuring the singlet. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 01 Jan 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1752632016-01-01T00:00:00Z
- Randomness in post-selected eventshttps://scholarbank.nus.edu.sg/handle/10635/175260Title: Randomness in post-selected events
Authors: Thinh L.P.; Torre G.D.L.; Bancal J.-D.; Pironio S.; Scarani V.
Abstract: Bell inequality violations can be used to certify private randomness for use in cryptographic applications. In photonic Bell experiments, a large amount of the data that is generated comes from no-detection events and presumably contains little randomness. This raises the question as to whether randomness can be extracted only from the smaller post-selected subset corresponding to proper detection events, instead of from the entire set of data. This could in principle be feasible without opening an analogue of the detection loophole as long as the min-entropy of the post-selected data is evaluated by taking all the information into account, including no-detection events. The possibility of extracting randomness from a short string has a practical advantage, because it reduces the computational time of the extraction. Here, we investigate the above idea in a simple scenario, where the devices and the adversary behave according to i.i.d. strategies. We show that indeed almost all the randomness is present in the pair of outcomes for which at least one detection happened. We further show that in some cases applying a pre-processing on the data can capture features that an analysis based on global frequencies only misses, thus resulting in the certification of more randomness. We then briefly consider non-i.i.d strategies and provide an explicit example of such a strategy that is more powerful than any i.i.d. one even in the asymptotic limit of infinitely many measurement rounds, something that was not reported before in the context of Bell inequalities. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 01 Jan 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1752602016-01-01T00:00:00Z
- Work production of quantum rotor engineshttps://scholarbank.nus.edu.sg/handle/10635/175118Title: Work production of quantum rotor engines
Authors: Colombo, M; Lòpez-Perolio, I; Meeks, H.D; Caleca, L; Parsons, M.T; Li, H; De Vecchi, G; Tudini, E; Foglia, C; Mondini, P; Manoukian, S; Behar, R; Garcia, E.B.G; Meindl, A; Montagna, M; Niederacher, D; Schmidt, A.Y; Varesco, L; Wappenschmidt, B; Bolla, M.K; Dennis, J; Michailidou, K; Wang, Q; Aittomäki, K; Andrulis, I.L; Anton-Culver, H; Arndt, V; Beckmann, M.W; Beeghly-Fadel, A; Benitez, J; Boeckx, B; Bogdanova, N.V; Bojesen, S.E; Bonanni, B; Brauch, H; Brenner, H; Burwinkel, B; Chang-Claude, J; Conroy, D.M; Couch, F.J; Cox, A; Cross, S.S; Czene, K; Devilee, P; Dörk, T; Eriksson, M; Fasching, P.A; Figueroa, J; Fletcher, O; Flyger, H; Gabrielson, M; García-Closas, M; Giles, G.G; González-Neira, A; Guénel, P; Haiman, C.A; Hall, P; Hamann, U; Hartman, M; Hauke, J; Hollestelle, A; Hopper, J.L; Jakubowska, A; Jung, A; Kosma, V.-M; Lambrechts, D; Le Marchand, L; Lindblom, A; Lubinski, J; Mannermaa, A; Margolin, S; Miao, H; Milne, R.L; Neuhausen, S.L; Nevanlinna, H; Olson, J.E; Peterlongo, P; Peto, J; Pylkäs, K; Sawyer, E.J; Schmidt, M.K; Schmutzler, R.K; Schneeweiss, A; Schoemaker, M.J; See, M.H; Southey, M.C; Swerdlow, A; Teo, S.H; Toland, A.E; Tomlinson, I; Truong, T; van Asperen, C.J; van den Ouweland, A.M.W; van der Kolk, L.E; Winqvist, R; Yannoukakos, D; Zheng, W; Dunning, A.M; Easton, D.F; Henderson, A; Hogervorst, F.B.L; Izatt, L; Offitt, K; Side, L.E; van Rensburg, E.J; Embrace, S; Hebon, S; McGuffog, L; Antoniou, A.C; Chenevix-Trench, G; Spurdle, A.B; Goldgar, D.E; Hoya, M.D.L; Radice, P; kConFab/AOCS Investigators; Seah, S; Nimmrichter, S; Scarani, V
Abstract: We study the mechanical performance of quantum rotor heat engines in terms of common notions of work using two prototypical models: a mill driven by the heat flow from a hot to a cold mode, and a piston driven by the alternate heating and cooling of a single working mode. We evaluate the extractable work in terms of ergotropy, the kinetic energy associated to net directed rotation, as well as the intrinsic work based on the exerted torque under autonomous operation, and we compare them to the energy output for the case of an external dissipative load and for externally driven engine cycles. Our results connect work definitions from both physical and information-theoretical perspectives. In particular, we find that apart from signatures of angular momentum quantization, the ergotropy is consistent with the intuitive notion of work in the form of net directed motion. It also agrees with the energy output to an external load or agent under optimal conditions. This sets forth a consistent thermodynamical description of rotating quantum motors, flywheels, and clocks. © 2018 The Author(s). Published by IOP Publishing Ltd on behalf of Deutsche Physikalische Gesellschaft.
Mon, 01 Jan 2018 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1751182018-01-01T00:00:00Z
- Measurement-device-independent quantification of entanglement for given Hilbert space dimensionhttps://scholarbank.nus.edu.sg/handle/10635/175272Title: Measurement-device-independent quantification of entanglement for given Hilbert space dimension
Authors: Goh, K.T; Bancal, J.-D; Scarani, V
Abstract: We address the question of how much entanglement can be certified from the observed correlations and the knowledge of the Hilbert space dimension of the measured systems. We focus on the case in which both systems are known to be qubits. For several correlations (though not for all), one can certify the same amount of entanglement as with state tomography, but with fewer assumptions, since nothing is assumed about the measurements. We also present security proofs of quantum key distribution (QKD) without any assumption on the measurements. We discuss how both the amount of entanglement and the security of QKD are affected by the inefficiency of detectors in this scenario. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 01 Jan 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1752722016-01-01T00:00:00Z
- Solving the scattering of N photons on a two-level atom without computationhttps://scholarbank.nus.edu.sg/handle/10635/175248Title: Solving the scattering of N photons on a two-level atom without computation
Authors: Roulet, A; Scarani, V
Abstract: We propose a novel approach for solving the scattering of light onto a two-level atom coupled to a one-dimensional waveguide. First we express the physical quantity of interest in terms of Feynman diagrams and treat the atom as a non-saturable linear beamsplitter. By using the atomic response to our advantage, a relevant substitution is then made that captures the nonlinearity of the atom, and the final result is obtained in terms of simple integrals over the initial incoming wavepackets. The procedure is not limited to post-scattering quantities and allows for instance to derive the atomic excitation during the scattering event. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 01 Jan 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1752482016-01-01T00:00:00Z
- All pure bipartite entangled states can be self-testedhttps://scholarbank.nus.edu.sg/handle/10635/174425Title: All pure bipartite entangled states can be self-tested
Authors: Coladangelo, A; Goh, K.T; Scarani, V
Abstract: Quantum technologies promise advantages over their classical counterparts in the fields of computation, security and sensing. It is thus desirable that classical users are able to obtain guarantees on quantum devices, even without any knowledge of their inner workings. That such classical certification is possible at all is remarkable: It is a consequence of the violation of Bell inequalities by entangled quantum systems. Device-independent self-testing refers to the most complete such certification: It enables a classical user to uniquely identify the quantum state shared by uncharacterized devices by simply inspecting the correlations of measurement outcomes. Self-testing was first demonstrated for the singlet state and a few other examples of self-testable states were reported in recent years. Here, we address the long-standing open question of whether every pure bipartite entangled state is self-testable. We answer it affirmatively by providing explicit self-testing correlations for all such states. © 2017 Japan Antibiotics Research Association All rights reserved.
Sun, 01 Jan 2017 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1744252017-01-01T00:00:00Z
- Focus on device independent quantum informationhttps://scholarbank.nus.edu.sg/handle/10635/179612Title: Focus on device independent quantum information
Authors: Pironio, S; Scarani, V; Vidick, T
Abstract: It is possible to devise quantum information protocols whose correctness can be certified even when they are run with untrusted quantum devices, on which no a priori assumptions are made. Hence the name 'device-independence' (DI) to refer to such protocols. It allows for certifiable cryptographic randomness generation (RNG) and key distribution (QKD) with unprecedented security. A promising path to the design of more experimentally friendly protocols is to make stronger assumptions on the devices, keeping the spirit of device independence while acknowledging differences in the level of trust about the quantum devices used that can be justified in the context of a realistic implementations. Practical implementations also reveal the limits of the device-independent model: as any model for security, device-independence makes a set of assumptions, such as perfect isolation of the trusted users' laboratories, that may in practice be compromised. Beyond key distribution, it is interesting to investigate if the device-independent approach to security can be extended to other tasks in multi-party cryptography.
Fri, 01 Jan 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1796122016-01-01T00:00:00Z
- Upper bounds for the security of two distributed-phase reference protocols of quantum cryptographyhttps://scholarbank.nus.edu.sg/handle/10635/98538Title: Upper bounds for the security of two distributed-phase reference protocols of quantum cryptography
Authors: Branciard, C.; Gisin, N.; Scarani, V.
Abstract: The differential-phase-shift (DPS) and the coherent-one-way (COW) are among the most practical protocols for quantum cryptography, and are therefore the object of fast-paced experimental developments. The assessment of their security is also a challenge for theorists: the existing tools, that allow to prove security against the most general attacks, do not apply to these two protocols in any straightforward way. We present new upper bounds for their security in the limit of large distances (d ≳ 50 km with typical values in optical fibers) by considering a large class of collective attacks, namely those in which the adversary attaches ancillary quantum systems to each pulse or to each pair of pulses. We introduce also two modified versions of the COW protocol, which may prove more robust than the original one. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 25 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985382008-01-25T00:00:00Z
- Reference-frame-independent quantum key distributionhttps://scholarbank.nus.edu.sg/handle/10635/97788Title: Reference-frame-independent quantum key distribution
Authors: Laing, A.; Scarani, V.; Rarity, J.G.; O'Brien, J.L.
Abstract: We describe a quantum key distribution protocol based on pairs of entangled qubits that generates a secure key between two partners in an environment of unknown and slowly varying reference frame. A direction of particle delivery is required, but the phases between the computational basis states need not be known or fixed. The protocol can simplify the operation of existing setups and has immediate applications to emerging scenarios such as earth-to-satellite links and the use of integrated photonic waveguides. We compute the asymptotic secret key rate for a two-qubit source, which coincides with the rate of the six-state protocol for white noise. We give the generalization of the protocol to higher-dimensional systems and detail a scheme for physical implementation in the three-dimensional qutrit case. © 2010 The American Physical Society.
Wed, 07 Jul 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977882010-07-07T00:00:00Z
- Testing the dimension of hilbert spaceshttps://scholarbank.nus.edu.sg/handle/10635/98241Title: Testing the dimension of hilbert spaces
Authors: Brunner, N.; Pironio, S.; Acin, A.; Gisin, N.; Méthot, A.A.; Scarani, V.
Abstract: Given a set of correlations originating from measurements on a quantum state of unknown Hilbert space dimension, what is the minimal dimension d necessary to describe such correlations? We introduce the concept of dimension witness to put lower bounds on d. This work represents a first step in a broader research program aiming to characterize Hilbert space dimension in various contexts related to fundamental questions and quantum information applications. © 2008 The American Physical Society.
Fri, 30 May 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/982412008-05-30T00:00:00Z
- One-sided device-independent quantum key distribution: Security, feasibility, and the connection with steeringhttps://scholarbank.nus.edu.sg/handle/10635/97433Title: One-sided device-independent quantum key distribution: Security, feasibility, and the connection with steering
Authors: Branciard, C.; Cavalcanti, E.G.; Walborn, S.P.; Scarani, V.; Wiseman, H.M.
Abstract: We analyze the security and feasibility of a protocol for quantum key distribution (QKD) in a context where only one of the two parties trusts his measurement apparatus. This scenario lies naturally between standard QKD, where both parties trust their measurement apparatuses, and device-independent QKD (DI-QKD), where neither do, and can be a natural assumption in some practical situations. We show that the requirements for obtaining secure keys are much easier to meet than for DI-QKD, which opens promising experimental opportunities. We clarify the link between the security of this one-sided DI-QKD scenario and the demonstration of quantum steering, in analogy to the link between DI-QKD and the violation of Bell inequalities. © 2012 American Physical Society.
Tue, 03 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974332012-01-03T00:00:00Z
- Testing quantum correlations versus single-particle properties within Leggett's model and beyondhttps://scholarbank.nus.edu.sg/handle/10635/115974Title: Testing quantum correlations versus single-particle properties within Leggett's model and beyond
Authors: Branciard, C.; Brunner, N.; Gisin, N.; Kurtsiefer, C.; Lamas-Linares, A.; Ling, A.; Scarani, V.
Abstract: Quantum theory predicts and experiments confirm that nature can produce correlations between distant events that are non-local in the sense of violating a Bell inequality. Nevertheless, Bell's strong sentence 'Correlations cry out for explanations' (ref. 2) remains relevant. The maturing of quantum information science and the discovery of the power of non-local correlations, for example for cryptographic key distribution beyond the standard quantum key distribution schemes, strengthen Bell's wish and make it even more timely. In 2003, Leggett proposed an alternative model for non-local correlations that he proved to be incompatible with quantum predictions. We present here a new approach to this model, along with new inequalities for testing it. These inequalities can be derived in a very simple way, assuming only the non-negativity of probability distributions; they are also stronger than previously published and experimentally tested Leggett-type inequalities. The simplest of the new inequalities is experimentally violated. Then we go beyond Leggett's model, and show that we cannot ascribe even partially defined individual properties to the components of a maximally entangled pair. © 2008 Macmillan Publishers Limited. All rights reserved.
Mon, 01 Sep 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1159742008-09-01T00:00:00Z
- Excitation of a single atom with exponentially rising light pulseshttps://scholarbank.nus.edu.sg/handle/10635/116334Title: Excitation of a single atom with exponentially rising light pulses
Authors: Aljunid, S.A.; Maslennikov, G.; Wang, Y.; Dao, H.L.; Scarani, V.; Kurtsiefer, C.
Abstract: We investigate the interaction between a single atom and optical pulses in a coherent state with a controlled temporal envelope. In a comparison between a rising exponential and a square envelope, we show that the rising exponential envelope leads to a higher excitation probability for fixed low average photon numbers, in accordance with a time-reversed Weisskopf-Wigner model. We characterize the atomic transition dynamics for a wide range of the average photon numbers and are able to saturate the optical transition of a single atom with ≈50 photons in a pulse by a strong focusing technique. © 2013 American Physical Society.
Tue, 03 Sep 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1163342013-09-03T00:00:00Z
- Bell tests with min-entropy sourceshttps://scholarbank.nus.edu.sg/handle/10635/52809Title: Bell tests with min-entropy sources
Authors: Thinh, L.P.; Sheridan, L.; Scarani, V.
Abstract: Device independent protocols rely on the violation of Bell inequalities to certify properties of the resources available. The violation of the inequalities is meaningless without a few well-known assumptions. One of these is measurement independence, the property that the source of the states measured in an inequality is uncorrelated from the measurements selected. Since this assumption cannot be confirmed, we consider the consequences of relaxing it and find that the definition chosen is critically important to the observed behavior. Considering a definition that is a bound on the min-entropy of the measurement settings, we find lower bounds on the min-entropy of the source used to choose the inputs required to deduce any quantum or nonlocal behavior from a Bell inequality violation. These bounds are significantly more restrictive than the ones obtained by endowing the measurement-input source with the further structure of a Santha-Vazirani source. We also outline a procedure for finding tight bounds and study the set of probabilities that can result from relaxing measurement dependence. © 2013 American Physical Society.
Tue, 25 Jun 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528092013-06-25T00:00:00Z
- Device-independent state estimation based on Bell's inequalitieshttps://scholarbank.nus.edu.sg/handle/10635/112417Title: Device-independent state estimation based on Bell's inequalities
Authors: Bardyn, C.-E.; Liew, T.C.H.; Massar, S.; McKague, M.; Scarani, V.
Abstract: The only information available about an alleged source of entangled quantum states is the amount S by which the Clauser-Horne-Shimony-Holt inequality is violated: nothing is known about the nature of the system or the measurements that are performed. We discuss how the quality of the source can be assessed in this black-box scenario, as compared to an ideal source that would produce maximally entangled states (more precisely, any state for which S=22). To this end, we present several inequivalent notions of fidelity, each one related to the use one can make of the source after having assessed it, and we derive quantitative bounds for each of them in terms of the violation S. We also derive a lower bound on the entanglement of the source as a function of S only. © 2009 The American Physical Society.
Mon, 14 Dec 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124172009-12-14T00:00:00Z
- Information science: Guaranteed randomnesshttps://scholarbank.nus.edu.sg/handle/10635/98979Title: Information science: Guaranteed randomness
Authors: Scarani, V.
Thu, 15 Apr 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989792010-04-15T00:00:00Z
- Tree-size complexity of multiqubit stateshttps://scholarbank.nus.edu.sg/handle/10635/98456Title: Tree-size complexity of multiqubit states
Authors: Nguyên, L.H.; Cai, Y.; Wu, X.; Scarani, V.
Abstract: Complexity is often invoked alongside size and mass as a characteristic of macroscopic quantum objects. In 2004, Aaronson introduced the tree size (TS) as a computable measure of complexity and studied its basic properties. In this paper, we improve and expand on those initial results. In particular, we give explicit characterizations of a family of states with superpolynomial complexity nΩ(logn)=TS=O(√n!) in the number of qubits n, and we show that any matrix-product state whose tensors are of dimension D×D has polynomial complexity TS=O(nlog22D). © 2013 American Physical Society.
Mon, 22 Jul 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984562013-07-22T00:00:00Z
- Finite-key analysis for practical implementations of quantum key distributionhttps://scholarbank.nus.edu.sg/handle/10635/96638Title: Finite-key analysis for practical implementations of quantum key distribution
Authors: Cai, R.Y.Q.; Scarani, V.
Abstract: The lists of bits processed in quantum key distribution are necessarily of finite length. The need for finite-key unconditional security bounds was recognized long ago, but the theoretical tools have become available only very recently. We provide finite-key unconditional security bounds for two practical implementations of the Bennett-Brassard 1984 coding: prepare- and-measure implementations without decoy states and entanglement-based implementations. A finite-key bound for prepare-and-measure implementations with decoy states is also derived under a simplified treatment of the statistical fluctuations. The presentation is tailored to allow direct application of the bounds in experiments. Finally, the bounds are also evaluated on a priori reasonable expected values of the observed parameters. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Thu, 30 Apr 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/966382009-04-30T00:00:00Z
- Large violation of Bell inequalities using both particle and wave measurementshttps://scholarbank.nus.edu.sg/handle/10635/117061Title: Large violation of Bell inequalities using both particle and wave measurements
Authors: Cavalcanti, D.; Brunner, N.; Skrzypczyk, P.; Salles, A.; Scarani, V.
Abstract: When separated measurements on entangled quantum systems are performed, the theory predicts correlations that cannot be explained by any classical mechanism: communication is excluded because the signal should travel faster than light; preestablished agreement is excluded because Bell inequalities are violated. All optical demonstrations of such violations have involved discrete degrees of freedom and are plagued by the detection-efficiency loophole. A promising alternative is to use continuous variables combined with highly efficient homodyne measurements. However, all the schemes proposed so far use states or measurements that are extremely difficult to achieve, or they produce very weak violations. We present a simple method to generate large violations for feasible states using both photon counting and homodyne detections. The present scheme can also be used to obtain nonlocality from easy-to-prepare Gaussian states (e.g., two-mode squeezed state). © 2011 American Physical Society.
Mon, 08 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1170612011-08-08T00:00:00Z
- Efficient excitation of a two-level atom by a single photon in a propagating modehttps://scholarbank.nus.edu.sg/handle/10635/116316Title: Efficient excitation of a two-level atom by a single photon in a propagating mode
Authors: Wang, Y.; Minář, J.; Sheridan, L.; Scarani, V.
Abstract: State mapping between atoms and photons, and photon-photon interactions play an important role in scalable quantum information processing. We consider the interaction of a two-level atom with a quantized propagating pulse in free space and study the probability Pe(t) of finding the atom in the excited state at any time t. This probability is expected to depend on (i) the quantum state of the pulse field and (ii) the overlap between the pulse and the dipole pattern of the atomic spontaneous emission. We show that the second effect is captured by a single parameter Λ[0,8π3], obtained by weighting the dipole pattern with the numerical aperture. Then, Pe(t) can be obtained by solving time-dependent Heisenberg-Langevin equations. We provide detailed solutions for both single-photon Fock state and coherent states and for various temporal shapes of the pulses. © 2011 American Physical Society.
Tue, 28 Jun 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1163162011-06-28T00:00:00Z
- Information-causality and extremal tripartite correlationshttps://scholarbank.nus.edu.sg/handle/10635/115152Title: Information-causality and extremal tripartite correlations
Authors: Yang, T.H.; Cavalcanti, D.; Almeida, M.L.; Teo, C.; Scarani, V.
Abstract: We study the principle of information-causality (IC) in the presence of extremal no-signaling correlations on a tripartite scenario. We prove that all, except one, of the non-local correlations lead to violation of IC. The remaining non-quantum correlation is shown to satisfy any bipartite physical principle. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1151522012-01-01T00:00:00Z
- Evaluation of two different entanglement measures on a bound entangled statehttps://scholarbank.nus.edu.sg/handle/10635/52920Title: Evaluation of two different entanglement measures on a bound entangled state
Authors: Branciard, C.; Zhu, H.; Chen, L.; Scarani, V.
Abstract: We consider the mixed three-qubit bound entangled state defined as the normalized projector on the subspace that is complementary to an unextendible product basis. Using the fact that no product state lies in the support of that state, we compute its entanglement by providing a basis of its subspace formed by "minimally entangled" states. The approach is in principle applicable to any entanglement measure; here we provide explicit values for both the geometric measure of entanglement and a generalized concurrence. © 2010 The American Physical Society.
Fri, 23 Jul 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529202010-07-23T00:00:00Z
- Tomographic quantum cryptography protocols are reference frame independenthttps://scholarbank.nus.edu.sg/handle/10635/53234Title: Tomographic quantum cryptography protocols are reference frame independent
Authors: Thinh, L.P.; Sheridan, L.; Scarani, V.
Abstract: We consider the class of reference frame independent protocols in d dimensions for quantum key distribution, in which Alice and Bob have one natural basis that is aligned and the rest of their measurement bases are unaligned. We relate existing approaches to tomographically complete protocols. We comment on two different approaches to finite key bounds in this setting, one direct and one using the entropic uncertainty relation and suggest that the existing finite key bounds can still be improved. © 2012 World Scientific Publishing Company.
Sun, 01 Apr 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/532342012-04-01T00:00:00Z
- Local content of bipartite qubit correlationshttps://scholarbank.nus.edu.sg/handle/10635/97082Title: Local content of bipartite qubit correlations
Authors: Branciard, C.; Gisin, N.; Scarani, V.
Abstract: One of the last open problems concerning two qubits in a pure state is to find the exact local content of their correlation, in the sense of Elitzur, Popescu, and Rohrlich (EPR2). We propose an EPR2 decomposition that allows us to prove, for a wide range of states |ψ(θ)=cosθ|00+sinθ|11, that their local content is pL̄(θ)=cos2θ. We also share reflections on how to possibly extend this result to all two-qubit pure states. © 2010 The American Physical Society.
Wed, 03 Feb 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970822010-02-03T00:00:00Z
- Device-independent quantum key distribution secure against collective attackshttps://scholarbank.nus.edu.sg/handle/10635/96213Title: Device-independent quantum key distribution secure against collective attacks
Authors: Pironio, S.; Acin, A.; Brunner, N.; Gisin, N.; Massar, S.; Scarani, V.
Abstract: Device-independent quantum key distribution (DIQKD) represents a relaxation of the security assumptions made in usual quantum key distribution (QKD). As in usual QKD, the security of DIQKD follows from the laws of quantum physics, but contrary to usual QKD, it does not rely on any assumptions about the internal working of the quantum devices used in the protocol. In this paper, we present in detail the security proof for a DIQKD protocol introduced in Acín et al (2008 Phys. Rev. Lett. 98 230501). This proof exploits the full structure of quantum theory (as opposed to other proofs that exploit only the no-signaling principle), but only holds against collective attacks, where the eavesdropper is assumed to act on the quantum systems of the honest parties independently and identically in each round of the protocol (although she can act coherently on her systems at any time). The security of any DIQKD protocol necessarily relies on the violation of a Bell inequality. We discuss the issue of loopholes in Bell experiments in this context. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Thu, 30 Apr 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/962132009-04-30T00:00:00Z
- Device-independent certification of the teleportation of a qubithttps://scholarbank.nus.edu.sg/handle/10635/96212Title: Device-independent certification of the teleportation of a qubit
Authors: Ho, M.; Bancal, J.-D.; Scarani, V.
Abstract: We want to certify in a black-box scenario that two parties simulating the teleportation of a qubit are really using quantum resources. If active compensation is part of the simulation, perfect teleportation can be faked by purely classical means. If active compensation is not implemented, a classical simulation is necessarily imperfect: In this case, we provide bounds for the certification of quantumness using only the observed statistics. In particular, if a uniform shrinking of the Bloch vector is observed on the teleported side, an average teleportation fidelity of 85% guarantees the use of quantum resources. In general, the criterion is not simply related to the fidelity; in an extreme case, the assessment of quantumness can be positive even for an average fidelity as low as 50%. © 2013 American Physical Society.
Mon, 18 Nov 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/962122013-11-18T00:00:00Z
- Multipartite fully nonlocal quantum stateshttps://scholarbank.nus.edu.sg/handle/10635/112464Title: Multipartite fully nonlocal quantum states
Authors: Almeida, M.L.; Cavalcanti, D.; Scarani, V.; Acín, A.
Abstract: We present a general method for characterizing the quantum correlations obtained after local measurements on multipartite systems. Sufficient conditions for a quantum system to be fully nonlocal according to a given partition, as well as being (genuinely) multipartite fully nonlocal, are derived. These conditions allow us to identify all completely connected graph states as multipartite fully nonlocal quantum states. Moreover, we show that this feature can also be observed in mixed states: the tensor product of five copies of the Smolin state, a biseparable and bound entangled state, is multipartite fully nonlocal. © 2010 The American Physical Society.
Mon, 17 May 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124642010-05-17T00:00:00Z
- Recovering part of the boundary between quantum and nonquantum correlations from information causalityhttps://scholarbank.nus.edu.sg/handle/10635/97776Title: Recovering part of the boundary between quantum and nonquantum correlations from information causality
Authors: Allcock, J.; Brunner, N.; Pawlowski, M.; Scarani, V.
Abstract: Recently, the principle of information causality has appeared as a good candidate for an information-theoretic principle that would single out quantum correlations among more general nonsignaling models. Here, we present results going in this direction, namely, we show that part of the boundary of quantum correlations actually emerges from information causality. © 2009 The American Physical Society.
Wed, 14 Oct 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977762009-10-14T00:00:00Z
- Entanglement and irreversibility in the approach to thermal equilibriumhttps://scholarbank.nus.edu.sg/handle/10635/99005Title: Entanglement and irreversibility in the approach to thermal equilibrium
Authors: Scarani, V.
Abstract: When a physical system is put in contact with a very large thermal bath, it undergoes a dissipative (i.e., an apparently irreversible) process that leads to thermal equilibrium. This dynamical process can be described fully within quantum physics, involving only unitary, therefore reversible, maps. The information, initially present in the system, is not erased, but is diluted in the bath because of entanglement. Irreversibility may arise if, after quantum information has been thus diluted, some classical information is lost. This paper reviews a model for thermalization that displays these features. Two new analytical results are provided for the zero-temperature channels: a new quantitative measure of entanglement, and a study of irreversibility in the case where the lost classical information is the label of the particles in the bath. © EDP Sciences/Societá Italiana di Fisica/Springer-Verlag 2007.
Sat, 01 Dec 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/990052007-12-01T00:00:00Z
- Security proof for quantum key distribution using qudit systemshttps://scholarbank.nus.edu.sg/handle/10635/53155Title: Security proof for quantum key distribution using qudit systems
Authors: Sheridan, L.; Scarani, V.
Abstract: We provide security bounds against coherent attacks for two families of quantum key distribution protocols that use d-dimensional quantum systems. In the asymptotic regime, both the secret key rate for fixed noise and the robustness to noise increase with d. The finite key corrections are found to be almost insensitive to d 20. © 2010 The American Physical Society.
Tue, 07 Sep 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/531552010-09-07T00:00:00Z
- Information causality as a physical principlehttps://scholarbank.nus.edu.sg/handle/10635/112453Title: Information causality as a physical principle
Authors: Pawłowski, M.; Paterek, T.; Kaszlikowski, D.; Scarani, V.; Winter, A.; Zukowski, M.
Abstract: Quantum physics has remarkable distinguishing characteristics. For example, it gives only probabilistic predictions (non-determinism) and does not allow copying of unknown states (no-cloning1). Quantum correlations may be stronger than any classical ones2, but information cannot be transmitted faster than light (no-signalling). However, these features do not uniquely define quantum physics. A broad class of theories exist that share such traits and allow even stronger (than quantum) correlations3. Here we introduce the principle of 'information causality' and show that it is respected by classical and quantum physics but violated by all no-signalling theories with stronger than (the strongest) quantum correlations. The principle relates to the amount of information that an observer (Bob) can gain about a data set belonging to another observer (Alice), the contents of which are completely unknown to him. Using all his local resources (which may be correlated with her resources) and allowing classical communication from her, the amount of information that Bob can recover is bounded by the information volume (m) of the communication. Namely, if Alice communicates m bits to Bob, the total information obtainable by Bob cannot be greater than m. For m = 0, information causality reduces to the standard nosignalling principle. However, no-signalling theories with maximally strong correlations would allow Bob access to all the data in any m-bit subset of the whole data set held by Alice. If only one bit is sent by Alice (m = 1), this is tantamount to Bob's being able to access the value of any single bit of Alice's data (but not all of them). Information causality may therefore help to distinguish physical theories from non-physical ones. We suggest that information causality - a generalization of the no-signalling condition - might be one of the foundational properties of nature. ©2009 Macmillan Publishers Limited. All rights reserved.
Thu, 22 Oct 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124532009-10-22T00:00:00Z
- More randomness from the same datahttps://scholarbank.nus.edu.sg/handle/10635/117078Title: More randomness from the same data
Authors: Bancal, J.-D.; Sheridan, L.; Scarani, V.
Abstract: Correlations that cannot be reproduced with local variables certify the generation of private randomness. Usually, the violation of a Bell inequality is used to quantify the amount of randomness produced. Here, we show how private randomness generated during a Bell test can be directly quantified from the observed correlations, without the need to process these data into an inequality. The frequency with which the different measurement settings are used during the Bell test can also be taken into account. This improved analysis turns out to be very relevant for Bell tests performed with a finite collection efficiency. In particular, applying our technique to the data of a recent experiment (Christensen et al 2013 Phys. Rev. Lett. 111 130406), we show that about twice as much randomness as previously reported can be potentially extracted from this setup. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1170782014-01-01T00:00:00Z
- Quantum Bell inequalities from macroscopic localityhttps://scholarbank.nus.edu.sg/handle/10635/53121Title: Quantum Bell inequalities from macroscopic locality
Authors: Yang, T.H.; Navascués, M.; Sheridan, L.; Scarani, V.
Abstract: We propose a method to generate analytical quantum Bell inequalities based on the principle of macroscopic locality. By imposing locality over binary processings of virtual macroscopic intensities, we establish a correspondence between Bell inequalities and quantum Bell inequalities in bipartite scenarios with dichotomic observables. We discuss how to improve the latter approximation and how to extend our ideas to scenarios with more than two outcomes per setting. © 2011 American Physical Society.
Mon, 14 Feb 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/531212011-02-14T00:00:00Z
- Cross time-bin photonic entanglement for quantum key distributionhttps://scholarbank.nus.edu.sg/handle/10635/96129Title: Cross time-bin photonic entanglement for quantum key distribution
Authors: Martin, A.; Kaiser, F.; Vernier, A.; Beveratos, A.; Scarani, V.; Tanzilli, S.
Abstract: We report a fully fibered source emitting cross time-bin-entangled photons at 1540 nm from type-II spontaneous parametric down-conversion. Compared to standard time-bin-entanglement realizations, the preparation interferometer requires no phase stabilization, simplifying its implementation in quantum key distribution experiments. Bell-type tests of such a cross time-bin state are performed in the Franson configuration and lead to two-photon interference raw visibilities greater than 95%, which are only limited by the dark counts in the detectors and imperfections in the analysis system. Just by trusting the randomness of the beam splitters, the correlations generated by the source can be proved of nonclassical origin even in a passive implementation. The obtained results confirm the suitability of this source for time-bin-based quantum key distribution. © 2013 American Physical Society.
Mon, 04 Feb 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/961292013-02-04T00:00:00Z
- Device-independent certification of entangled measurementshttps://scholarbank.nus.edu.sg/handle/10635/112416Title: Device-independent certification of entangled measurements
Authors: Rabelo, R.; Ho, M.; Cavalcanti, D.; Brunner, N.; Scarani, V.
Abstract: We present a device-independent protocol to test if a given black-box measurement device is entangled, that is, has entangled eigenstates. Our scheme involves three parties and is inspired by entanglement swapping; the test uses the Clauser-Horne-Shimony-Holt Bell inequality, checked between each pair of parties. In the case where all particles are qubits, we characterize quantitatively the deviation of the measurement device from a perfect Bell-state measurement. © 2011 American Physical Society.
Mon, 25 Jul 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124162011-07-25T00:00:00Z
- Quantum non-locality based on finite-speed causal influences leads to superluminal signallinghttps://scholarbank.nus.edu.sg/handle/10635/97695Title: Quantum non-locality based on finite-speed causal influences leads to superluminal signalling
Authors: Bancal, J.-D.; Pironio, S.; Acín, A.; Liang, Y.-C.; Scarani, V.; Gisin, N.
Abstract: The experimental violation of Bell inequalities using space-like separated measurements precludes the explanation of quantum correlations through causal influences propagating at subluminal speed. Yet, any such experimental violation could always be explained in principle through models based on hidden influences propagating at a finite speed v>c, provided v is large enough. Here, we show that for any finite speed v with c < v < ∞, such models predict correlations that can be exploited for faster-than-light communication. This superluminal communication does not require access to any hidden physical quantities, but only the manipulation of measurement devices at the level of our present-day description of quantum experiments. Hence, assuming the impossibility of using non-local correlations for superluminal communication, we exclude any possible explanation of quantum correlations in terms of influences propagating at any finite speed. Our result uncovers a new aspect of the complex relationship between multipartite quantum non-locality and the impossibility of signalling. © 2012 Macmillan Publishers Limited. All rights reserved.
Sat, 01 Dec 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976952012-12-01T00:00:00Z
- Experimentally faking the violation of Bell's inequalitieshttps://scholarbank.nus.edu.sg/handle/10635/52926Title: Experimentally faking the violation of Bell's inequalities
Authors: Gerhardt, I.; Liu, Q.; Lamas-Linares, A.; Skaar, J.; Scarani, V.; Makarov, V.; Kurtsiefer, C.
Abstract: Entanglement witnesses such as Bell inequalities are frequently used to prove the nonclassicality of a light source and its suitability for further tasks. By demonstrating Bell inequality violations using classical light in common experimental arrangements, we highlight why strict locality and efficiency conditions are not optional, particularly in security-related scenarios. © 2011 American Physical Society.
Thu, 20 Oct 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529262011-10-20T00:00:00Z
- Analysis of a proposal for a realistic loophole-free Bell test with atom-light entanglementhttps://scholarbank.nus.edu.sg/handle/10635/116224Title: Analysis of a proposal for a realistic loophole-free Bell test with atom-light entanglement
Authors: Teo, C.; Minář, J.; Cavalcanti, D.; Scarani, V.
Abstract: The violation of Bell inequalities where both detection and locality loopholes are closed is crucial for device-independent assessments of quantum information. While of a technological nature, the simultaneous closing of both loopholes still remains a challenge. In Teo, a realistic setup to produce an atom-photon entangled state that could reach a loophole-free Bell inequality violation within current experimental technology is proposed. Here we improve the analysis of this proposal by giving an analytical treatment that shows that the state proposed in Teo can violate a Bell inequality for arbitrarily low photodectection efficiency, when all other losses are ignored. Moreover, it is also able to violate a Bell inequality considering only atomic and homodyne measurements eliminating the need to consider inefficient photocounting measurements. In this case, the maximum Clauser-Horne-Shimony-Holt inequality violation achievable is 2.29, and the minimum transmission required for violation is about 68%. Finally, we show that by postselecting on an atomic measurement, one can engineer superpositions of coherent states for various coherent state amplitudes. © 2013 American Physical Society.
Wed, 27 Nov 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1162242013-11-27T00:00:00Z
- Ultrafast quantum gates in circuit QEDhttps://scholarbank.nus.edu.sg/handle/10635/98502Title: Ultrafast quantum gates in circuit QED
Authors: Romero, G.; Ballester, D.; Wang, Y.M.; Scarani, V.; Solano, E.
Abstract: We present a method to implement ultrafast two-qubit gates valid for the ultrastrong coupling and deep strong coupling regimes of light-matter interaction, considering state-of-the-art circuit quantum electrodynamics technology. Our proposal includes a suitable qubit architecture and is based on a four-step sequential displacement of the intracavity field, operating at a time proportional to the inverse of the resonator frequency. Through ab initio calculations, we show that these quantum gates can be performed at subnanosecond time scales while keeping a fidelity above 99%. © 2012 American Physical Society.
Mon, 19 Mar 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985022012-03-19T00:00:00Z
- Interfacing light and single atoms with a lenshttps://scholarbank.nus.edu.sg/handle/10635/53000Title: Interfacing light and single atoms with a lens
Authors: Tey, M.K.; Maslennikov, G.; Liew, T.C.H.; Aljunid, S.A.; Huber, F.; Chng, B.; Chen, Z.; Scarani, V.; Kurtsiefer, C.
Abstract: We characterize the interaction between a single atom or similar microscopic system and a light field via the scattering ratio. For this, we first derive the electrical field in a strongly focused Gaussian light beam, and then consider the atomic response. Following the simple scattering model, the fraction of scattered optical power for a weak coherent probe field leads to unphysical scattering ratios above 1 in the strong focusing regime. A refined model considering interference between the exciting and scattered field into finitesized detectors or optical fibers is presented, and compared with experimental extinction measurements for various focusing strengths. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Tue, 07 Apr 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/530002009-04-07T00:00:00Z
- The non-locality of n noisy Popescu-Rohrlich boxeshttps://scholarbank.nus.edu.sg/handle/10635/98301Title: The non-locality of n noisy Popescu-Rohrlich boxes
Authors: Fitzi, M.; Hänggi, E.; Scarani, V.; Wolf, S.
Abstract: We quantify the amount of non-locality contained in n noisy versions of the so-called Popescu-Rohrlich boxes (PRBs), i.e. bipartite systems violating the CHSH Bell inequality maximally. Following the approach by Elitzur, Popescu and Rohrlich, we measure the amount of non-locality of a system by representing it as a convex combination of a local behaviour, with maximal possible weight, and a non-signalling system. We show that the local part of n systems, each of which approximates a PRB with probability 1 - ε, is of order Θ(ε⌈n/2⌉) in the isotropic, and equal to (3ε)n in the maximally biased case. © 2010 IOP Publishing Ltd.
Fri, 19 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983012010-11-19T00:00:00Z
- Effects of reduced measurement independence on bell-based randomness expansionhttps://scholarbank.nus.edu.sg/handle/10635/112425Title: Effects of reduced measurement independence on bell-based randomness expansion
Authors: Koh, D.E.; Hall, M.J.W.; Setiawan; Pope, J.E.; Marletto, C.; Kay, A.; Scarani, V.; Ekert, A.
Abstract: With the advent of quantum information, the violation of a Bell inequality is used to witness the absence of an eavesdropper in cryptographic scenarios such as key distribution and randomness expansion. One of the key assumptions of Bell's theorem is the existence of experimental "free will," meaning that measurement settings can be chosen at random and independently by each party. The relaxation of this assumption potentially shifts the balance of power towards an eavesdropper. We consider a no-signaling model with reduced "free will" and bound the adversary's capabilities in the task of randomness expansion. © 2012 American Physical Society.
Thu, 18 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124252012-10-18T00:00:00Z
- Physical characterization of quantum devices from nonlocal correlationshttps://scholarbank.nus.edu.sg/handle/10635/127985Title: Physical characterization of quantum devices from nonlocal correlations
Authors: Bancal J.-D.; Navascues M.; Scarani V.; Vertesi T.; Yang T.H.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1279852015-01-01T00:00:00Z
- Quantum cryptography with finite resources: Unconditional security bound for discrete-variable protocols with one-way postprocessinghttps://scholarbank.nus.edu.sg/handle/10635/97669Title: Quantum cryptography with finite resources: Unconditional security bound for discrete-variable protocols with one-way postprocessing
Authors: Scarani, V.; Renner, R.
Abstract: We derive a bound for the security of quantum key distribution with finite resources under one-way postprocessing, based on a definition of security that is composable and has an operational meaning. While our proof relies on the assumption of collective attacks, unconditional security follows immediately for standard protocols such as Bennett-Brassard 1984 and six-states protocol. For single-qubit implementations of such protocols, we find that the secret key rate becomes positive when at least N∼105 signals are exchanged and processed. For any other discrete-variable protocol, unconditional security can be obtained using the exponential de Finetti theorem, but the additional overhead leads to very pessimistic estimates. © 2008 The American Physical Society.
Thu, 22 May 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976692008-05-22T00:00:00Z
- Finite-key security against coherent attacks in quantum key distributionhttps://scholarbank.nus.edu.sg/handle/10635/52939Title: Finite-key security against coherent attacks in quantum key distribution
Authors: Sheridan, L.; Le, T.P.; Scarani, V.
Abstract: Christandl et al (2009 Phys. Rev. Lett. 102 020504) provide, in particular, the possibility of studying unconditional security in the finite-key regime for all discrete-variable protocols. We spell out this bound from their general formalism. Then, we apply it in the analysis of a recently proposed protocol (Laing et al 2010 Phys. Rev. A 82 012304). This protocol is meaningful when the alignment of Alice's and Bob's reference frames is not monitored and may vary with time. In this scenario, the notion of asymptotic key rate has hardly any operational meaning, because if one waits too long a time, the average correlations are smeared out and no security can be inferred. Therefore, finitekey analysis is necessary for finding the maximal achievable secret key rate and the corresponding optimal number of signals. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Wed, 01 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529392010-12-01T00:00:00Z
- Simulation of partial entanglement with nonsignaling resourceshttps://scholarbank.nus.edu.sg/handle/10635/97932Title: Simulation of partial entanglement with nonsignaling resources
Authors: Brunner, N.; Gisin, N.; Popescu, S.; Scarani, V.
Abstract: With the goal of gaining a deeper understanding of quantum nonlocality, we decompose quantum correlations into more elementary nonlocal correlations. We show that the correlations of all pure entangled states of two qubits can be simulated without communication, hence using only no-signaling resources. Our simulation model works in two steps. First, we decompose the quantum correlations into a local and a nonlocal part. Second, we present a model for simulating the nonlocal part using only no-signaling resources. In our model partially entangled states require more nonlocal resources than maximally entangled states, but the less the state is entangled, the less frequently must the nonlocal resources be used. © 2008 The American Physical Society.
Thu, 13 Nov 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979322008-11-13T00:00:00Z
- Quantum networks reveal quantum nonlocalityhttps://scholarbank.nus.edu.sg/handle/10635/116555Title: Quantum networks reveal quantum nonlocality
Authors: Cavalcanti, D.; Almeida, M.L.; Scarani, V.; Acín, A.
Abstract: The results of local measurements on some composite quantum systems cannot be reproduced classically. This impossibility, known as quantum nonlocality, represents a milestone in the foundations of quantum theory. Quantum nonlocality is also a valuable resource for information-processing tasks, for example, quantum communication, quantum key distribution, quantum state estimation or randomness extraction. Still, deciding whether a quantum state is nonlocal remains a challenging problem. Here, we introduce a novel approach to this question: we study the nonlocal properties of quantum states when distributed and measured in networks. We show, using our framework, how any one-way entanglement distillable state leads to nonlocal correlations and prove that quantum nonlocality is a non-additive resource, which can be activated. There exist states, local at the single-copy level, that become nonlocal when taking several copies of them. Our results imply that the nonlocality of quantum states strongly depends on the measurement context. © 2011 Macmillan Publishers Limited. All rights reserved.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1165552011-01-01T00:00:00Z
- Strong Constraints on Models that Explain the Violation of Bell Inequalities with Hidden Superluminal Influenceshttps://scholarbank.nus.edu.sg/handle/10635/125036Title: Strong Constraints on Models that Explain the Violation of Bell Inequalities with Hidden Superluminal Influences
Authors: Scarani, V.; Bancal, J.-D.; Suarez, A.; Gisin, N.
Abstract: We discuss models that attempt to provide an explanation for the violation of Bell inequalities at a distance in terms of hidden influences. These models reproduce the quantum correlations in most situations, but are restricted to produce local correlations in some configurations. The argument presented in (Bancal et al. Nat Phys 8:867, 2012) applies to all of these models, which can thus be proved to allow for faster-than-light communication. In other words, the signalling character of these models cannot remain hidden. © 2014 Springer Science+Business Media New York.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1250362014-01-01T00:00:00Z
- Realistic loophole-free Bell test with atom-photon entanglementhttps://scholarbank.nus.edu.sg/handle/10635/116563Title: Realistic loophole-free Bell test with atom-photon entanglement
Authors: Teo, C.; Araújo, M.; Quintino, M.T.; Minář, J.; Cavalcanti, D.; Scarani, V.; Terra Cunha, M.; França Santos, M.
Abstract: The establishment of nonlocal correlations, guaranteed through the violation of a Bell inequality, is not only important from a fundamental point of view but constitutes the basis for device-independent quantum information technologies. Although several nonlocality tests have been conducted so far, all of them suffered from either locality or detection loopholes. Among the proposals for overcoming these problems are the use of atom-photon entanglement and hybrid photonic measurements (for example, photodetection and homodyning). Recent studies have suggested that the use of atom-photon entanglement can lead to Bell inequality violations with moderate transmission and detection efficiencies. Here we combine these ideas and propose an experimental setup realizing a simple atom-photon entangled state that can be used to obtain nonlocality when considering realistic experimental parameters including detection efficiencies and losses due to required propagation distances. © 2013 Macmillan Publishers Limited. All rights reserved.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1165632013-01-01T00:00:00Z