Ultracold atoms for foundational tests of quantum mechanics

Lewis-Swan, Robert J.

doi:10.14264/uql.2016.12

Cited by 3 publications

(3 citation statements)

References 148 publications

(444 reference statements)

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“…In this case, the results of the uniform model, while being applicable to peak amplitudes of correlation functions for nonuniform systems, cannot address the quantitative details of the decay of these correlations with distance. Such details can be addressed numerically using stochastic approaches in phase-space [44,[46][47][48][49][50] or analytic approaches based on perturbation theory [39,40,[50][51][52], which are, however, beyond the scope of this work.…”

Section: S3mentioning

confidence: 99%

Solving the Quantum Many-Body Problem via Correlations Measured with a Momentum Microscope

et al. 2017

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In quantum many-body theory, all physical observables are described in terms of correlation functions between particle creation or annihilation operators. Measurement of such correlation functions can therefore be regarded as an operational solution to the quantum many-body problem. Here, we demonstrate this paradigm by measuring multiparticle momentum correlations up to third order between ultracold helium atoms in an s-wave scattering halo of colliding Bose-Einstein condensates, using a quantum manybody momentum microscope. Our measurements allow us to extract a key building block of all higherorder correlations in this system-the pairing field amplitude. In addition, we demonstrate a record violation of the classical Cauchy-Schwarz inequality for correlated atom pairs and triples. Measuring multiparticle momentum correlations could provide new insights into effects such as unconventional superconductivity and many-body localization. DOI: 10.1103/PhysRevLett.118.240402 In quantum physics, fully understanding and characterizing complex systems, comprising a large (often macroscopic) number of interacting particles, is an extremely challenging problem. Solutions within the standard framework of (first-quantized) quantum mechanics generally require the knowledge of the full quantum many-body wave function. This necessitates an exponentially large amount of information to be encoded and simulated using the many-body Schrödinger equation. In an equivalent (second-quantized) quantum field theory formulation, the fundamental understanding of quantum many-body systems comes through the description of all physical observables via correlation functions between particle creation and annihilation operators. Here, the exponential complexity of the quantum many-body problem is converted into the need to know all possible multiparticle correlation functions, starting from two-, three-, and increasing to arbitrary N-particle (or higher-order) correlations.From an experimental viewpoint, an operational solution to the quantum many-body problem is therefore equivalent to measuring all multiparticle correlations. In certain cases, however, knowing only a specific set of (few-body or lower-order) correlations is sufficient to allow a solution of the many-body problem to be constructed. This was recently shown for phase correlations between two coupled one-dimensional (1D) Bose gases [1]. Apart from facilitating the description of physical observables, characterizing multiparticle correlations is important for introducing controlled approximations in many-body physics, such as the virial-and related cluster-expansion approaches that rely on truncation of the Bogolyubov-Born-GreenKirkwood-Yvon hierarchy [2,3] Correlations between multiple photons are also routinely used in numerous quantum optics experiments including ghost imaging [15,16], defining criteria for nonclassicality [17,18], analyzing entangled states generated by parametric down conversion [19], and characterizing single photon sources [20].Here, we demonstrate an e...

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Section: S3mentioning

confidence: 99%

Solving the Quantum Many-Body Problem via Correlations Measured with a Momentum Microscope

et al. 2017

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“…(4) describes the widely studied phenomena of spontaneous optical parametric down-conversion. This process is known to produce the two-mode squeezed vacuum state [39,40], which exibits strong correlations between the down-converted particles. Whilst this simplification is not valid in the system under investigation, due to the absence of a true condensate in 1D, we still expect strong, non-trivial correlations in the downconverted field due to the pair-wise nature of the scattering process.…”

Section: B Correlation Functionsmentioning

confidence: 99%

Atomic twin beams and violation of a motional-state Bell inequality from a phase-fluctuating quasicondensate source

Lewis-Swan

Kheruntsyan

2020

Phys. Rev. A

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We investigate the dynamics of atomic twin beams produced from a phase-fluctuating source, specifically a 1D Bose gas in the quasi-condensate regime, motivated by the experiment reported in Nature Physics 7, 608 (2011). A short-time analytic model is constructed, which is a modified version of the undepleted pump approximation widely used in quantum and atom optics, except that here we take into account the initial phase fluctuations of the pump source as opposed to assuming long-range phase coherence. We use this model to make quantitative and qualitative predictions of how phase-fluctuations of the source impact the two-particle correlations of scattered atom-pairs. The model is benchmarked against detailed numerical simulations using stochastic phase-space methods, and is shown to validate the intuitive notion that the broadening of momentum-space correlation functions between atoms scattered from a quasi-condensate is driven by the broadened momentum width of the source compared to a true phase coherent condensate. Finally, we combine these theoretical tools and results to investigate the effect phase fluctuations of the twin-beam source can have on a proposed demonstration of a violation of a Bell inequality, which intrinsically relies on phase-sensitive pair correlations. arXiv:2002.01998v1 [cond-mat.quant-gas]

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“…Later applications included large-scale truncated Wigner simulations of BEC collisions [20], simulated quantum transport in a BEC in an optical lattice [21], detailed comparison of experiment and theory for optical fiber, to below the quantum noise level [22], comparisons of 3D positive-P and Wigner simulations of BEC collisions with 150,000 atoms from first principles [10], proposals for atomic Hong-Ou-Mandel correlations from BEC collisions [23], violations of Bell inequalities [24,25], and many other applications [9].…”

Section: Phase-space Representationsmentioning

confidence: 99%

Initial states and apodisation for quantum field simulations in phase-space

Drummond

2019

Preprint

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Bosonic quantum fields can be simulated with "quantum software" in phase-space. The positive-P, Wigner and Q-function phase-space methods are reviewed. Initial quantum states and boundaries for infinite domains are considered in detail. The quantum initial conditions treated include both multi-mode Gaussian states and number states, which are sampled using phase-shifted weighting techniques. This is more efficient than direct probabilistic sampling. Algorithms for treating periodic boundaries within infinite domains are developed via apodisation, or absorbers near the boundary. Similar truncation or anti-aliasing issues arise in the frequency domain with Fourier transform methods. Complex apodisation, in which there are phase-shifts as well as absorption, improves accuracy by reducing unwanted errors, and this is illustrated numerically. The complex power law apodisation techniques described here can be applied to numerical calculations or even directly in optics. Phase-space simulations, used for both quantum optical and Bose-Einstein condensate quantum dynamical calculations, require quantum noise terms to be included. A method is described to analyze number conservation in apodised calculations. Some techniques developed here are potentially applicable to all digital simulations, whether using classical or quantum logic.

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Ultracold atoms for foundational tests of quantum mechanics

Cited by 3 publications

References 148 publications

Solving the Quantum Many-Body Problem via Correlations Measured with a Momentum Microscope

Solving the Quantum Many-Body Problem via Correlations Measured with a Momentum Microscope

Atomic twin beams and violation of a motional-state Bell inequality from a phase-fluctuating quasicondensate source

Initial states and apodisation for quantum field simulations in phase-space

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