arXiv subjects

A. Auyuanet

Publications and source records attributed to A. Auyuanet.

12 recordsLinked to original sources

arXiv2023

Bell non-locality in two-mode Gaussian states revealed via local squeezing

Local unitary transforms cannot affect the quantum correlations between two systems sharing an entangled state although they do influence the outcomes of local measurements. By considering local squeezing operations we introduce an extended family of observables allowing violation of the CHSH Bell inequality for two-mode Gaussian systems. We show that local squeezing can enable or enhance the identification of non-local two-mode states. In particular, we show that local squeezing followed by photons/no-photons discrimination can suffice to reveal non-locality in a broad ensemble of pure and mixed two-mode Gaussian states.

quant-ph↗

arXiv2020

Entanglement-Coherence and Discord-Coherence analytical relations for X states

In this work we derive analytical relations between Entanglement and Coherence as well as between Discord and Coherence, for Bell-diagonal states and for X states, evolving under the action of several noise channels: Bit Flip, Phase Damping and Depolarizing. We demonstrate that for these families, Coherence is the fundamental correlation, that is: Coherence is necessary for the presence of Entanglement and Discord.

quant-ph↗

arXiv2018

Full statistics of ideal homodyne detection using real (noisy) local oscillator

We show that the full statistics of the two detectors outputs in a balanced homodyne detection setup involving a local oscillator in an ideal coherent state is experimentally accessible despite the excess noise existing in actual laser sources. This possibility is illustrated using phase randomized coherent states signals from which the statistics of Fock states can accurately be obtained. The experimental verification of the recently predicted [Kühn and Vogel, Phys. Rev. A, \textbf{98}, 013832 (2018)] two-detector correlation probability for Fock states is presented for states $\vert 1 \rangle$ and $\vert 2 \rangle$.

quant-ph↗

arXiv2017

Direct-dynamical entanglement-discord relations

In this article, by considering Bell-diagonal two-qubit initial states submitted to local dynamics generated by the phase damping, bit flip, phase flip, bit-phase flip, and depolarizing channels, we report some elegant direct-dynamical relations between geometric measures of entanglement and discord. The complex scenario appearing already in this simplified case study indicates that similarly simple relation shall hardly be found in more general situations.

quant-ph↗

arXiv2015

Experimental characterization of the Gaussian state of squeezed light obtained via single-passage through an atomic vapor

We show that the description of light in terms of Stokes operators in combination with the assumption of Gaussian statistics results in a dramatic simplification of the experimental study of fluctuations in the light transmitted through an atomic vapor: no local oscillator is required, the detected quadrature is easily selected by a wave-plate angle and the complete noise ellipsis reconstruction is obtained via matrix diagonalization. We provide empirical support for the assumption of Gaussian statistics in quasi-resonant light transmitted through an $^{87}$Rb vapor cell and we illustrate the suggested approach by studying the evolution of the fluctuation ellipsis as a function of laser detuning. Applying the method to two light beams obtained by parting squeezed light in a beamsplitter, we have measured entanglement and quantum discord.

quant-ph↗

arXiv2014

Vectorial atomic magnetometer based on coherent transients of laser absorption in Rb vapor

We have designed and tested an atomic vectorial magnetometer based on the analysis of the coherent oscillatory transients in the transmission of resonant laser light through a Rb vapor cell. We show that the oscillation amplitudes at the Larmor frequency and its first harmonic are related through a simple formula to the angles determining the orientation of the magnetic field vector. The magnetometer was successfully applied to the measurement of the ambient magnetic field.

physics.atom-ph↗

arXiv2007

Sub-ballistic behaviour of the Quantum Kicked Rotor

We study the resonances of the quantum kicked rotor subjected to an excitation that follows an aperiodic Fibonacci prescription. In such a case the secondary resonances show a sub-ballistic behaviour like the quantum walk with the same aperiodic prescription for the coin. The principal resonances maintain the well-known ballistic behaviour. Then the parallelism previusly established between the kicked rotor and the generalized quantum walk is retained only with the secondary resonances.

quant-ph↗

arXiv2006

Quantum search algorithm as an open system

We study the quantum search algorithm as an open system. More specifically, we analyze the responses of that algorithm to an external monochromatic field, and to the decoherences introduced by the measurement process. We find that the search algorithm is robust with respect to many external interactions.

quant-ph↗

arXiv2005

Quantum search with resonances

We present a continuous time quantum search algorithm analogous to Grover's. In particular, the optimal search time for this algorithm is proportional to $\sqrt{N}$, where $N$ is the database size. This search algorithm can be implemented using any Hamiltonian with a discrete energy spectrum through excitation of resonances between an initial and the searched state. This algorithm is robust and, as in the case of Grover's, it allows for an error $O(1/\sqrt{N})$ in the determination of the searched state. A discrete time version of this continuous time search algorithm is built, and the connection between the search algorithms with discrete and continuous times is established.

quant-ph↗

arXiv2004

Generalized Quantum Walk in Momentum Space

We consider a new model of quantum walk on a one-dimensional momentum space that includes both discrete jumps and continuous drift. Its time evolution has two stages; a Markov diffusion followed by localized dynamics. As in the well known quantum kicked rotor, this model can be mapped into a localized one-dimensional Anderson model. For exceptional (rational) values of its scale parameter, the system exhibits resonant behavior and reduce to the usual discrete time quantum walk on the line.

quant-ph↗

arXiv2004

Decoherence in the quantum walk on the line

We investigate the quantum walk on the line when decoherences are introduced either through simultaneous measurements of the chirality and particle position, or as a result of broken links. Both mechanisms drive the system to a classical diffusive behavior. In the case of measurements, we show that the diffusion coefficient is proportional to the variance of the initially localized quantum random walker just before the first measurement. When links between neighboring sites are randomly broken with probability $p$ per unit time, the evolution becomes decoherent after a characteristic time that scales as $1/p$. The fact that the quadratic increase of the variance is eventually lost even for very small frequencies of disrupting events, suggests that the implementation of a quantum walk on a real physical system may be severely limited by thermal noise and lattice imperfections.

quant-ph↗

arXiv2004

Quantum random walk on the line as a markovian process

We analyze in detail the discrete--time quantum walk on the line by separating the quantum evolution equation into Markovian and interference terms. As a result of this separation, it is possible to show analytically that the quadratic increase in the variance of the quantum walker's position with time is a direct consequence of the coherence of the quantum evolution. If the evolution is decoherent, as in the classical case, the variance is shown to increase linearly with time, as expected. Furthermore we show that this system has an evolution operator analogous to that of a resonant quantum kicked rotor. As this rotator may be described through a quantum computational algorithm, one may employ this algorithm to describe the time evolution of the quantum walker.

quant-ph↗