arXiv subjects

P. Navez

Publications and source records attributed to P. Navez.

10 recordsLinked to original sources

arXiv2022

Quantum electrodynamics of non-demolition detection of single microwave photon by superconducting qubit array

By consistently applying the formalism of quantum electrodynamics we developed a comprehensive theoretical framework describing the interaction of single microwave photons with an array of superconducting transmon qubits in a wave guide cavity resonator. In particular, we analyze the effects of microwave photons on the arrays response to a weak probe signal exciting the resonator. The study reveals that a high quality factor cavities provide better spectral resolution of the response, while cavities with moderate quality factor allow better sensitivity for a single photon detection. Remarkably, our analysis showed that a single-photon signal can be detected by even a sole qubit in cavity under the realistic range of system parameters. We also discuss how quantum properties of the photons and electrodynamical properties of resonators affect the response of qubits array. Our results provide an efficient theoretical background for informing the development and design of quantum devices consisting of arrays of qubits, especially for those using a cavity where an explicit expression for the transmission or reflection is required.

quant-ph↗

arXiv2020

Towards the Heisenberg limit in microwave photon detection by a qubit array

Using an analytically solvable model, we show that a qubit array-based detector allows to achieve the fundamental Heisenberg limit in detecting single photons. In case of superconducting qubits, this opens new opportunities for quantum sensing and communications in the important microwave range.

quant-ph↗

arXiv2016

Propagation of quantum fluctuations in quantum Ising model

We investigate the entanglement dynamics between two distant qubits by analyzing correlations in the quantum Ising model. Starting from the spin system in a paramagnetic regime enforced by the external magnetic field $B$, we then switch on the ferromagnetic spin-spin coupling $J$. Using the large coordination number expansion, we consider two limiting switching regimes: (1) adiabatic, which monitors the evolution of the ground state through the quantum transition to an ordered state; and (2) instantaneous (quench) which monitors instead the propagation of quantum fluctuations and simulates the generation of long range correlations. In particular, we find that quantum fluctuations propagate with twice the group speed of excitations in the equilibrium state of the system.

cond-mat.stat-mech↗

arXiv2014

Propagation of quantum correlations after a quench in the Mott-insulator regime of the Bose-Hubbard model

We study a quantum quench in the Bose-Hubbard model where the tunneling rate $J$ is suddenly switched from zero to a finite value in the Mott regime. In order to solve the many-body quantum dynamics far from equlibrium, we consider the reduced density matrices for a finite number (one, two, three, etc.) of lattice sites and split them up into on-site density operators, i.e., the mean field, plus two-point and three-point correlations etc. Neglecting three-point and higher correlations, we are able to numerically simulate the time-evolution of the few-site density matrices and the two-point quantum correlations (e.g., their effective light-cone structure) for a comparably large number ${\cal O}(10^3)$ of lattice sites.

quant-ph↗

arXiv2014

Phase diagram of quasi-two-dimensional bosons in laser speckle potential

We have studied the phase diagram of a quasi-two-dimensional interacting Bose gas at zero temperature in the presence of random potential created by laser speckles. The superfluid fraction and the fraction of particles with zero momentum are obtained within the mean-field Gross-Pitaevskii theory and in diffusion Monte Carlo simulations. We find a transition from the superfluid to the insulating state, when the strength of the disorder grows. Estimations of the critical parameters are compared with the predictions of the percolation theory in the Thomas-Fermi approximation. Analytical expressions for the zero-momentum fraction and the superfluid fraction are derived in the limit of weak disorder and weak interactions within the framework of the Bogoliubov theory. Limits of validity of various approximations are discussed.

cond-mat.quant-gas↗

arXiv2014

Equilibration and prethermalization in the Bose-Hubbard and Fermi-Hubbard models

We study the Bose and Fermi Hubbard model in the (formal) limit of large coordination numbers $Z\gg1$. Via an expansion into powers of $1/Z$, we establish a hierarchy of correlations which facilitates an approximate analytical derivation of the time-evolution of the reduced density matrices for one and two sites etc. With this method, we study the quantum dynamics (starting in the ground state) after a quantum quench, i.e., after suddenly switching the tunneling rate $J$ from zero to a finite value, which is still in the Mott regime. We find that the reduced density matrices approach a (quasi) equilibrium state after some time. For one lattice site, this state can be described by a thermal state (within the accuracy of our approximation). However, the (quasi) equilibrium state of the reduced density matrices for two sites including the correlations cannot be described by a thermal state. Thus, real thermalization (if it occurs) should take much longer time. This behavior has already been observed in other scenarios and is sometimes called ``pre-thermalization.'' Finally, we compare our results to numerical simulations for finite lattices in one and two dimensions and find qualitative agreement.

quant-ph↗

arXiv2006

Magnetically tuned spin dynamics resonance

We present the experimental observation of a magnetically tuned resonance phenomenon resulting from spin mixing dynamics of ultracold atomic gases. In particular we study the magnetic field dependence of spin conversion in F=2 87Rb spinor condensates in the crossover from interaction dominated to quadratic Zeeman dominated dynamics. We discuss the observed phenomenon in the framework of spin dynamics as well as matter wave four wave mixing. Furthermore we show that the validity range of the single mode approximation for spin dynamics is significantly extended in the regime of high magnetic field.

cond-mat.other↗

arXiv2005

Evolution of a spinor condensate: coherent dynamics, dephasing and revivals

We present measurements and a theoretical model for the interplay of spin dependent interactions and external magnetic fields in atomic spinor condensates. We highlight general features like quadratic Zeeman dephasing and its influence on coherent spin mixing processes by focusing on a specific coherent superposition state in a F=1 $^{87}$Rb Bose-Einstein condensate. In particular, we observe the transition from coherent spinor oscillations to thermal equilibration.

cond-mat.other↗

arXiv2005

Cloning quantum entanglement in arbitrary dimensions

We have found a quantum cloning machine that optimally duplicates the entanglement of a pair of $d$-dimensional quantum systems. It maximizes the entanglement of formation contained in the two copies of any maximally-entangled input state, while preserving the separability of unentangled input states. Moreover, it cannot increase the entanglement of formation of all isotropic states. For large $d$, the entanglement of formation of each clone tends to one half the entanglement of the input state, which corresponds to a classical behavior. Finally, we investigate a local entanglement cloner, which yields entangled clones with one fourth the input entanglement in the large-$d$ limit.

quant-ph↗

arXiv2004

The optimal cloning of quantum coherent states is non-Gaussian

We consider the optimal cloning of quantum coherent states with single-clone and joint fidelity as figures of merit. Both optimal fidelities are attained for phase space translation covariant cloners. Remarkably, the joint fidelity is maximized by a Gaussian cloner, whereas the single-clone fidelity can be enhanced by non-Gaussian operations: a symmetric non-Gaussian 1-to-2 cloner can achieve a single-clone fidelity of approximately 0.6826, perceivably higher than the optimal fidelity of 2/3 in a Gaussian setting. This optimal cloner can be realized by means of an optical parametric amplifier supplemented with a particular source of non-Gaussian bimodal states. Finally, we show that the single-clone fidelity of the optimal 1-to-infinity cloner, corresponding to a measure-and-prepare scheme, cannot exceed 1/2. This value is achieved by a Gaussian scheme and cannot be surpassed even with supplemental bound entangled states.

quant-ph↗