arXiv subjects

L. Rosales-Zárate

Publications and source records attributed to L. Rosales-Zárate.

8 recordsLinked to original sources

arXiv2020

Testing macroscopic local realism using cat-states and Bell inequalities in time

We show how one may test macroscopic local realism where, different from conventional Bell tests, all relevant measurements need only distinguish between two macroscopically distinct states of the system being measured. Here, measurements give macroscopically distinguishable outcomes for a system observable and do not resolve microscopic properties (of order $\hbar$). Macroscopic local realism assumes: (1) macroscopic realism (the system prior to measurement is in a state which will lead to just one of the macroscopically distinguishable outcomes) and (2) macroscopic locality (a measurement on a system at one location cannot affect the macroscopic outcome of the measurement on a system at another location, if the measurement events are spacelike separated). To obtain a quantifiable test, we define $M$-scopic local realism where the outcomes are separated by an amount $\sim M$. We first show for $N$ up to $20$ that $N$-scopic Bell violations are predicted for entangled superpositions of $N$ bosons (at each of two sites). Secondly, we show violation of $M$-scopic local realism for entangled superpositions of coherent states of amplitude $α$, for arbitrarily large $M=α$. In both cases, the systems evolve dynamically according to a local nonlinear interaction. The first uses nonlinear beam splitters realised through nonlinear Josephson interactions; the second is based on nonlinear Kerr interactions. To achieve the Bell violations, the traditional choice between two spin measurement settings is replaced by a choice between different times of evolution at each site.

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arXiv2019

Mesoscopic two-mode entangled and steerable states of 40,000 atoms in a Bose-Einstein condensate interferometer

Using criteria based on superselection rules, we analyze the quantum correlations between the two condensate modes of the Bose-Einstein condensate interferometer of Egorov et al. [Phys. Rev. A 84, 021605 (2011)]. In order to determine the two-mode correlations, we develop a multi-mode theory that describes the dynamics of the condensate atoms and the thermal fraction through the interferometer sequence, in agreement with the experimentally measured fringe visibility. We thus present experimental evidence for two-mode entangled states genuinely involving 40,000 ^{87}Rb atoms, and for two-way steerability between two groups of 20,000 indistinguishable atoms.

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arXiv2018

Quantum software for linear photonic simulations

The search for new, application-specific quantum computers designed to outperform any classical computer is driven by the ending of Moore's law and the quantum advantages potentially obtainable. Photonic networks are promising examples, with experimental demonstrations and potential for obtaining a quantum computer to solve problems believed classically impossible. This introduces a challenge: how does one design or understand such photonic networks? We develop novel complex phase-space software for simulating these photonic networks, and apply this to boson sampling experiments. Our techniques give sampling errors orders of magnitude lower than experimental measurements of correlations, for the same number of samples. We show that these techniques remove systematic errors in previous algorithms for estimating correlations, with order of magnitude improvements in errors in some cases. In addition to that, we obtain a scalable channel-combination strategy for assessment of boson sampling devices.

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arXiv2017

Quantifying the mesoscopic quantum coherence of approximate NOON states and spin-squeezed two-mode Bose-Einstein condensates

We examine how to signify and quantify the mesoscopic quantum coherence of approximate two-mode NOON states and spin-squeezed two-mode Bose-Einstein condensates (BEC). We identify two criteria that verify a nonzero quantum coherence between states with quantum number different by $n$. These criteria negate certain mixtures of quantum states, thereby signifying a generalised $n$-scopic Schrodinger cat-type paradox. The first criterion is the correlation $\langle\hat{a}^{\dagger n}\hat{b}^{n}\rangle\neq0$ (here $\hat{a}$ and $\hat{b}$ are the boson operators for each mode). The correlation manifests as interference fringes in $n$-particle detection probabilities and is also measurable via quadrature phase amplitude and spin squeezing measurements. Measurement of $\langle\hat{a}^{\dagger n}\hat{b}^{n}\rangle$ enables a quantification of the overall $n$-th order quantum coherence, thus providing an avenue for high efficiency verification of a high-fidelity photonic NOON states. The second criterion is based on a quantification of the measurable spin-squeezing parameter $ξ_{N}$. We apply the criteria to theoretical models of NOON states in lossy interferometers and double-well trapped BECs. By analysing existing BEC experiments, we demonstrate generalised atomic "kitten" states and atomic quantum coherence with $n\gtrapprox10$ atoms.

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arXiv2016

Monogamy inequalities for entanglement using continuous variable measurements

We consider three modes $A$, $B$ and $C$ and derive continuous variable monogamy inequalities that constrain the distribution of bipartite entanglement amongst the three modes. The inequalities hold for all such tripartite states, without the assumption of Gaussian states, and are based on measurements of two conjugate quadrature phase amplitudes $X_{i}$ and $P_{i}$ at each mode $i=A,B$. The first monogamy inequality is $D_{BA}+D_{BC}\geq1$ where $D_{BA}<1$ is the widely used symmetric entanglement criterion, for which $D_{BA}$ is the sum of the variances of $(X_{A}-X_{B})/2$ and $(P_{A}+P_{B})/2$. A second monogamy inequality is $Ent_{BA}Ent_{BC}\geq\frac{1}{\left(1+(g_{BA}^{(sym)})^{2}\right)\left(1+(g_{BC}^{(sym)})^{2}\right)}$ where $Ent_{BA}<1$ is the EPR variance product criterion for entanglement. Here $Ent_{BA}$ is a normalised product of variances of $X_{B}-g_{BA}^{(sym)}X_{A}$ and $P_{B}+g_{BA}^{(sym)}P_{A}$, and $g_{BA}^{(sym)}$ is a parameter that gives a measure of the symmetry between the moments of $A$ and $B$. We also show that the monogamy bounds are increased if a standard steering criterion for the steering of $B$ is not satisfied. We illustrate the monogamy for continuous variable tripartite entangled states including the effects of losses and noise, and identify regimes of saturation of the inequalities. The monogamy relations explain the experimentally observed saturation at $D_{AB}=0.5$ for the entanglement between $A$ and $B$ when both modes have 50\% losses, and may be useful to establish rigorous bounds of correlation for the purpose of quantum key distribution protocols.

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arXiv2016

Leggett-Garg tests of macro-realism for multi-particle systems including double-well Bose-Einstein condensates

We construct quantifiable generalisations of Leggett-Garg tests for macro/ mesoscopic realism and noninvasive measurability that apply when not all outcomes of measurement can be identified as arising from one of two macroscopically distinguishable states. We show how quantum mechanics predicts a negation of the LG premises for proposals involving ideal-negative-result, weak and quantum non-demolition measurements on dynamical entangled systems, as might be realised with two-well Bose-Einstein condensates, path-entangled NOON states and atom interferometers.

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arXiv2016

Signifying the nonlocality of NOON states using Einstein-Podolsky-Rosen steering inequalities

We construct Einstein-Podolsky-Rosen (EPR) steering signatures for the nonlocality of the entangled superposition state described by $\frac{1}{\sqrt{2}}\{|N\rangle|0\rangle+|0\rangle|N\rangle\}$, called the two-mode NOON state. The signatures are a violation of an EPR steering inequality based on an uncertainty relation. The violation confirms an EPR steering between the two modes and involves certification of an inter-mode correlation for number, as well as quadrature phase amplitude measurements. We also explain how the signatures certify an $N$th order quantum coherence, so the system (for larger $N$) can be signified to be in a superposition of states distinct by a mesoscopic value of the two-mode quantum number difference. Finally, we examine the limitations imposed for lossy scenarios, discussing how experimental realisations may be possible for $N=2,3$.

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arXiv2015

Decoherence of Einstein-Podolsky-Rosen steering

We consider two systems A and B that share Einstein-Podolsky-Rosen (EPR) steering correlations and study how these correlations will decay, when each of the systems are independently coupled to a reservoir. EPR steering is a directional form of entanglement, and the measure of steering can change depending on whether the system A is steered by B, or vice versa. First, we examine the decay of the steering correlations of the two-mode squeezed state. We find that if the system B is coupled to a reservoir, then the decoherence of the steering of A by B is particularly marked, to the extent that there is a sudden death of steering after a finite time. We find a different directional effect, if the reservoirs are thermally excited. Second, we study the decoherence of the steering of a Schrödinger cat state, modeled as the entangled state of a spin and harmonic oscillator, when the macroscopic system (the cat) is coupled to a reservoir.

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