48 research outputs found
A many-body heat engine at criticality
We show that a quantum Otto cycle in which the medium, an interacting
ultracold gas, is driven between a superfluid and an insulating phase can
outperform similar single particle cycles. The presence of an energy gap
between the two phases can be used to improve performance, while the interplay
between lattice forces and the particle distribution can lead to a many-body
cooperative effect. Since finite time driving of this cycle can create unwanted
non-equilibrium dynamics which can significantly impair the performance of the
engine cycle, we also design an approximate shortcut to adiabaticity for the
many-body state that can be used to achieve an efficient Otto cycle around a
critical point.Comment: Includes Supplementary Material
A Feshbach engine in the Thomas-Fermi regime
Bose-Einstein condensates can be used to produce work by tuning the strength
of the interparticle interactions with the help of Feshbach resonances. In
inhomogeneous potentials, these interaction ramps change the volume of the
trapped gas allowing one to create a thermodynamic cycle known as the Feshbach
engine. However, in order to obtain a large power output, the engine strokes
must be performed on a short timescale, which is in contrast with the fact that
the efficiency of the engine is reduced by irreversible work if the strokes are
done in a non-adiabatic fashion. Here we investigate how such an engine can be
run in the Thomas-Fermi regime and present a shortcut to adiabaticity that
minimizes the irreversible work and allows for efficient engine operation.Comment: 8 pages, 7 figure
Correlations in low dimensional quantum systems
In this thesis I present the work done during my PhD in the area of low dimensional quantum gases. The chapters of this thesis are self contained and represent individual projects which have been peer reviewed and accepted for publication in respected international journals. Various systems are considered, the first of which is a two particle model which possesses an exact analytical solution. I investigate the non-classical correlations that exist between the particles as a function of the tunable properties of the system. In the second work I consider the coherences and out of equilibrium dynamics of a one-dimensional Tonks-Girardeau gas. I show how the coherence of the gas can be inferred from various properties of the reduced state and how this may be observed in experiments. I then present a model which can be used to probe a one-dimensional Fermi gas by performing a measurement on an impurity which interacts with the gas. I show how this system can be used to observe the so-called orthogonality catastrophe using modern interferometry techniques. In the next chapter I present a simple scheme to create superposition states of particles with special emphasis on the NOON state. I explore the effect of inter-particle interactions in the process and then characterise the usefulness of these states for interferometry. Finally I present my contribution to a project on long distance entanglement generation in ion chains. I show how carefully tuning the environment can create decoherence-free subspaces which allows one to create and preserve entanglement
Quenching small quantum gases: Genesis of the orthogonality catastrophe
We study the dynamics of two strongly interacting bosons with an additional
impurity atom trapped in a harmonic potential. Using exact numerical
diagonalization we are able to fully explore the dynamical evolution when the
interaction between the two distinct species is suddenly switched on
(quenched). We examine the behavior of the densities, the entanglement, the
Loschmidt echo and the spectral function for a large range of inter-species
interactions and find that even in such small systems evidence of Anderson's
orthogonality catastrophe can be witnessed.Comment: 6 pages, 5 figures, Accepted for publication in Physical Review
An efficient non-linear Feshbach engine
We investigate a thermodynamic cycle using a Bose-Einstein condensate with
nonlinear interactions as the working medium. Exploiting Feshbach resonances to
change the interaction strength of the BEC allows us to produce work by
expanding and compressing the gas. To ensure a large power output from this
engine these strokes must be performed on a short timescale, however such
non-adiabatic strokes can create irreversible work which degrades the engine's
efficiency. To combat this, we design a shortcut to adiabaticity which can
achieve an adiabatic-like evolution within a finite time, therefore
significantly reducing the out-of-equilibrium excitations in the BEC. We
investigate the effect of the shortcut to adiabaticity on the efficiency and
power output of the engine and show that the tunable nonlinearity strength,
modulated by Feshbach resonances, serves as a useful tool to enhance the
system's performance.Comment: 8 pages, 5 figures. To Appear New J. Phys. Focus on Shortcuts to
Adiabaticit
Static and dynamic phases of a Tonks-Girardeau gas in an optical lattice
We investigate the properties of a Tonks-Girardeau gas in the presence of a
one-dimensional lattice potential. Such a system is known to exhibit a pinning
transition when the lattice is commensurate with the particle density, leading
to the formation of an insulating state even at infinitesimally small lattice
depths. Here we examine the properties of the gas at all lattices depths and,
in addition to the static properties, also consider the non-adiabatic dynamics
induced by the sudden motion of the lattice potential with a constant speed.
Our work provides a continuum counterpart to the work done in discrete lattice
models.Comment: 24 pages, 12 figure
Interaction enhanced quantum heat engine
We study a minimal quantum Otto heat engine, where the working medium
consists of an interacting few-body system in a harmonic trap. This allows us
to consider the interaction strength as an additional tunable parameter during
the work strokes. We calculate the figures of merit of this engine as a
function of the temperature and show clearly in which parameter regimes the
interactions assist in engine performance. We also study the finite time
dynamics and the subsequent trade-off between the efficiency and the power,
comparing the interaction enhanced cycle with the case where the system remains
scale-invariant.Comment: 9 pages, 8 figure
Fermionization of a Few-Body Bose System Immersed into a Bose-Einstein Condensate
We study the recently introduced self-pinning transition [Phys. Rev. Lett.
128, 053401 (2022)] in a quasi-one-dimensional two-component quantum gas in the
case where the component immersed into the Bose-Einstein condensate has a
finite intraspecies interaction strength. As a result of the matter-wave
backaction, the fermionization in the limit of infinite intraspecies repulsion
occurs via a first-order phase transition to the self-pinned state, which is in
contrast to the asymptotic behavior in static trapping potentials. The system
also exhibits an additional superfluid state for the immersed component if the
interspecies interaction is able to overcome the intraspecies repulsion. We
approximate the superfluid state in an analytical model and derive an
expression for the phase transition line that coincides with well-known phase
separation criteria in binary Bose systems. The full phase diagram of the
system is mapped out numerically for the case of two and three atoms in the
immersed component.Comment: 13 pages, 4 figure