Asymmetric steering is an effect whereby an inseparable bipartite system can be found to be described by either quantum mechanics or local hidden variable theories depending on which one of Alice or Bob makes the required measurements. We show that, even with an inseparable bipartite system, situations can arise where Gaussian measurements on one half are not sufficient to answer the fundamental question of which theory gives an adequate description and the whole system must be considered. This phenomenon is possible because of an asymmetry in the definition of the original Einstein-Podolsky-Rosen paradox and in this article we show theoretically that it may be demonstrated, at least in the case where Alice and Bob can only make Gaussian measurements, using the intracavity nonlinear coupler.
Tensor network states are powerful variational Ansätze for many-body ground states of quantum lattice models. The use of Monte Carlo sampling techniques in tensor network approaches significantly reduces the cost of tensor contractions, potentially leading to a substantial increase in computational efficiency. Previous proposals are based on a Markov chain Monte Carlo scheme generated by locally updating configurations and, as such, must deal with equilibration and autocorrelation times, which result in a reduction of efficiency. Here we propose perfect sampling schemes, with vanishing equilibration and autocorrelation times, for unitary tensor networks, namely, tensor networks based on efficiently contractible, unitary quantum circuits, such as unitary versions of the matrix product state (MPS) and tree tensor network (TTN), and the multiscale entanglement renormalization Ansatz (MERA). Configurations are directly sampled according to their probabilities in the wave function, without resorting to a Markov chain process. We consider both complete sampling, involving all the relevant sites of the system, and incomplete sampling, which only involves a subset of those sites and which can result in a dramatic (basis-dependent) reduction of sampling error.
We propose three criteria for identifying continuous variable entanglement between two many-particle systems with no restrictions on the quantum state of the local oscillators used in the measurements. Mistakenly asserting a coherent state for the local oscillator can lead to incorrectly identifying the presence of entanglement. We demonstrate this in simulations with 100 particles and also find that large number fluctuations do not prevent the observation of entanglement. Our results are important for quantum information experiments with realistic Bose-Einstein condensates or in optics with arbitrary photon states. The study of the quantum properties of matter waves is a rapidly developing field known as quantum atom optics ͓1,2͔. Already several experiments have observed nonclassical effects in ultracold gases, including the Hanbury BrownTwiss effect for bosons ͓3͔, antibunching for fermions ͓4͔, sub-Poissonian number fluctuations ͓5͔, and density correlations from molecular dissociation ͓6͔ and in the Mottinsulator regime in an optical lattice ͓7͔. Although impressive achievements, the experimental techniques utilized in these observations are insufficient to detect quantum squeezing or entanglement. The demonstration of entanglementwhich Schrödinger described as being the central mystery of quantum mechanics ͓8͔-will be an important step toward quantum information applications of ultracold atomic systems.In quantum optical systems continuous variable ͑CV͒ entanglement can be demonstrated experimentally by measuring certain correlation functions of electromagnetic field quadratures and finding that these violate an inequality for separability ͓9,10͔ or an inequality ͓11͔ for demonstrating the Einstein-Podolsky-Rosen ͑EPR͒ paradox ͓12͔. For a number of systems, these quadratures can only be determined using homodyne or heterodyne measurement techniques and require a coherent state local oscillator-a highly occupied mode of the electromagnetic field that is a good approximation to the output of many lasers ͓13͔. Such measurements have led to the observation of optical squeezing ͓14,15͔ and the EPR paradox with photons ͓16͔, and have been used to perform quantum-state tomography ͓17͔ and continuous variable teleportation ͓18͔.In principle, squeezed or entangled atomic fields can be generated by atomic four-wave mixing ͓19-21͔, molecular disassociation ͓22͔, or mapping photon statistics onto atoms ͓23͔. Entanglement generated in these situations can potentially be used as a resource for quantum information ͓24͔. However, to unequivocally demonstrate entanglement between matter waves, it will be necessary to perform measurements sensitive to the relative phase of atomic wave packets. In principle, it is possible to measure matter-wave quadratures in direct analogy to the optical case using atomic measurements with a suitable local oscillator ͑phase reference͒ ͓25,26͔, of which the matter-wave equivalent is a BoseEinstein condensate. However, these are typically not large, with a maximum of 10 8 particles ͓27͔, and...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.