arXiv subjects

Joel F. Corney

Publications and source records attributed to Joel F. Corney.

12 recordsLinked to original sources

arXiv2026

Benchmarking quantum phase-space methods for near-resonant light propagation

We study the dynamics of light interacting with a near-resonant atomic medium using the truncated Wigner and positive P phase-space representations. The atomic degrees of freedom are described using the Jordan-Schwinger mapping. The dynamics is first analyzed under unitary evolution and subsequently in the presence of an optical reservoir. While both approaches capture the main features of the light-matter dynamics, we find that the truncated Wigner approximation exhibits noticeable deviations for stronger interaction strengths and when reservoir-induced noise becomes significant.

quant-ph↗

arXiv2022

Observation of robust polarization squeezing via the Kerr nonlinearity in an optical fibre

Squeezed light is one of the resources of photonic quantum technology. Among the various nonlinear interactions capable of generating squeezing, the optical Kerr effect is particularly easy-to-use. A popular venue is to generate polarization squeezing, which is a special self-referencing variant of two-mode squeezing. To date, polarization squeezing generation setups have been very sensitive to fluctuations of external factors and have required careful tuning. In this work, we report on a development of a new all-fibre setup for polarization squeezing generation. The setup consists of passive elements only and is simple, robust, and stable. We obtained more than 5 dB of directly measured squeezing over long periods of time without any need for adjustments. Thus, the new scheme provides a robust and easy to set up way of obtaining squeezed light applicable to different applications. We investigate the impact of pulse duration and pulse power on the degree of squeezing.

quant-ph↗

arXiv2020

Thermalisation in a Bose-Hubbard dimer with modulated tunneling

The periodically modulated Bose-Hubbard dimer model offers an experimentally realizable and highly tunable platform for observing the scrambling of quantum information and the apparent thermalisation of isolated, interacting quantum many-body systems. In this work we apply fidelity out-of-time-order correlators to establish connections between thermalisation in Floquet system, the exponential growth of FOTOCs as quantified by a non-zero quantum Lyapunov exponent, and the underlying classical transition from regular to chaotic dynamics in the dimer. Moreover, we demonstrate that a non-zero quantum Lyapunov exponent can also be inferred from measures quantifying the delocalisation of the Floquet modes of the system such as the Shannon entropy, which approaches unity if the system thermalises to the periodic Gibbs ensemble prediction.

quant-ph↗

arXiv2013

Improving Polarisation Squeezing In Sagnac Interferometer Configuration Using Photonic Crystal Fibre

The greater confinement of light that is possible in photonic crystal fibres leads to a greater effective nonlin- earity, which promises to yield greater quantum squeezing than is possible in standard optical fibre. However, experimental work to date has not achieved improvements over standard fibre. We present a comprehensive numerical investigation of polarisation squeezing in photonic crystal fibre in a Sagnac configuration. By including loss, a non-instantaneous Raman response, excess phase-noise, second- and third-order dispersion and self-steepening, the simulations are able to identify the physical factors that limit current photonic crystal fibre squeezing experiments.

quant-ph↗

arXiv2010

Finite temperature correlations in the Bose-Hubbard model: application of the Gauge $P$ representation

We study ultracold Bose gases in periodic potentials as described by the Bose-Hubbard model. In 1D and at finite temperature, we simulate ultracold Bose gases in imaginary time with the gauge $P$ representation. We study various quantities including the Luttinger parameter $K$, which is important for locating the boundaries of the Mott insulator lobes, and find a simple relation for the kinetic energy part of the Bose-Hubbard Hamiltonian. We show that for J=0, the stepwise pattern of the average number of particles per lattice site versus the chemical potential vanishes at temperatures above $T \approx 0.1 U$. Also, at chemical potential $μ=0.5 U$ and temperature $T=0.5 U$ by increasing $J$, the relative value of the number fluctuation decreases and approaches that of a coherent state.

cond-mat.quant-gas↗

arXiv2008

Simulations and Experiments on Polarisation Squeezing in Optical Fibre

We investigate polarisation squeezing of ultrashort pulses in optical fibre, over a wide range of input energies and fibre lengths. Comparisons are made between experimental data and quantum dynamical simulations, to find good quantitative agreement. The numerical calculations, performed using both truncated Wigner and exact $+P$ phase-space methods, include nonlinear and stochastic Raman effects, through coupling to phonons variables. The simulations reveal that excess phase noise, such as from depolarising GAWBS, affects squeezing at low input energies, while Raman effects cause a marked deterioration of squeezing at higher energies and longer fibre lengths. The optimum fibre length for maximum squeezing is also calculated.

quant-ph↗

arXiv2008

Hybrid phase-space simulation method for interacting Bose fields

We introduce an approximate phase-space technique to simulate the quantum dynamics of interacting bosons. With the future goal of treating Bose-Einstein condensate systems, the method is designed for systems with a natural separation into highly occupied (condensed) modes and lightly occupied modes. The method self-consistently uses the Wigner representation to treat highly occupied modes and the positive-P representation for lightly occupied modes. In this method, truncation of higher-derivative terms from the Fokker-Planck equation is usually necessary. However, at least in the cases investigated here, the resulting systematic error, over a finite time, vanishes in the limit of large Wigner occupation numbers. We tested the method on a system of two interacting anharmonic oscillators, with high and low occupations, respectively. The Hybrid method successfully predicted atomic quadratures to a useful simulation time 60 times longer than that of the positive-P method. The truncated Wigner method also performed well in this test. For the prediction of the correlation in a quantum nondemolition measurement scheme, for this same system, the Hybrid method gave excellent agreement with the exact result, while the truncated Wigner method showed a large systematic error.

quant-ph↗

arXiv2007

Raman-induced limits to efficient squeezing in optical fibers

We report new experiments on polarization squeezing using ultrashort photonic pulses in a single pass of a birefringent fiber. We measure what is to our knowledge a record squeezing of -6.8 +/- 0.3 dB in optical fibers which when corrected for linear losses is -10.4 +/- 0.8 dB. The measured polarization squeezing as a function of optical pulse energy, which spans a wide range from 3.5-178.8 pJ, shows a very good agreement with the quantum simulations and for the first time we see the experimental proof that Raman effects limit and reduce squeezing at high pulse energy.

quant-ph↗

arXiv2005

Monte Carlo techniques for real-time quantum dynamics

The stochastic-gauge representation is a method of mapping the equation of motion for the quantum mechanical density operator onto a set of equivalent stochastic differential equations. One of the stochastic variables is termed the "weight", and its magnitude is related to the importance of the stochastic trajectory. We investigate the use of Monte Carlo algorithms to improve the sampling of the weighted trajectories and thus reduce sampling error in a simulation of quantum dynamics. The method can be applied to calculations in real time, as well as imaginary time for which Monte Carlo algorithms are more-commonly used. The method is applicable when the weight is guaranteed to be real, and we demonstrate how to ensure this is the case. Examples are given for the anharmonic oscillator, where large improvements over stochastic sampling are observed.

quant-ph↗

arXiv2003

Gaussian quantum operator representation for bosons

We introduce the Gaussian quantum operator representation, using the most general multi-mode Gaussian operator basis. The representation unifies and substantially extends existing phase-space representations of density matrices for Bose systems, and also includes generalized squeezed-state and thermal bases. It enables first-principles dynamical or equilibrium calculations in quantum many-body systems, with quantum uncertainties appearing as dynamical objects. Any quadratic Liouville equation for the density operator results in a purely deterministic time evolution. Any cubic or quartic master equation can be treated using stochastic methods.

quant-ph↗

arXiv2001

Accurate switching intensities and length scales in quasi-phase-matched materials

We consider unseeded Type I second-harmonic generation in quasi-phase-matched (QPM) quadratic nonlinear materials and derive an accurate analytical expression for the evolution of the average intensity. The intensity-dependent nonlinear phase mismatch due to the QPM induced cubic nonlinearity is found. The equivalent formula for the intensity for maximum conversion, the crossing of which changes the nonlinear phase-shift of the fundamental over a period abruptly by $π$, corrects earlier estimates by more than a factor of 5. We find the crystal lengths necessary to obtain an optimal flat phase versus intensity response on either side of this separatrix intensity.

nlin.PS↗

arXiv2000

Solitons in quadratic nonlinear photonic crystals

We study solitons in one-dimensional quadratic nonlinear photonic crystals with modulation of both the linear and nonlinear susceptibilities. We derive averaged equations that include induced cubic nonlinearities and numerically find previously unknown soliton families. The inclusion of the induced cubic terms enables us to show that solitons still exist even when the effective quadratic nonlinearity vanishes and conventional theory predicts that there can be no soliton. We demonstrate that both bright and dark forms of these solitons are stable under propagation.

nlin.PS↗