arXiv subjects

A. J. Daley

Publications and source records attributed to A. J. Daley.

At least 37 records · Page 2Linked to original sources

arXiv2011

Spatial Pauli-blocking of spontaneous emission in optical lattices

Spontaneous emission by an excited fermionic atom can be suppressed due to the Pauli exclusion principle if the relevant final states after the decay are already occupied by identical atoms in the ground state. Here we discuss a setup where a single atom is prepared in the first excited state on a single site of an optical lattice under conditions of very tight trapping. We investigate these phenomena in the context of two experimental realizations: (1) with alkali atoms, where the decay rate of the excited state is large and (2) with alkaline earth-like atoms, where the decay rate from metastable states can be tuned in experiments. This phenomenon has potential applications towards reservoir engineering and dissipative many-body state preparation in an optical lattice.

quant-ph↗

arXiv2011

Precision Measurements on a Tunable Mott Insulator of Ultracold Atoms

We perform precision measurements on a Mott-insulator quantum state of ultracold atoms with tunable interactions. We probe the dependence of the superfluid-to-Mott-insulator transition on the interaction strength and explore the limits of the standard Bose-Hubbard model description. By tuning the on-site interaction energies to values comparable to the interband separation, we are able to quantitatively measure number-dependent shifts in the excitation spectrum caused by effective multi-body interactions.

quant-ph↗

arXiv2011

Dynamical crystal creation with polar molecules or Rydberg atoms in optical lattices

We investigate the dynamical formation of crystalline states with systems of polar molecules or Rydberg atoms loaded into a deep optical lattice. External fields in these systems can be used to couple the atoms or molecules between two internal states: one that is weakly interacting and one that exhibits a strong dipole-dipole interaction. By appropriate time variation of the external fields, we show that it is possible to produce crystalline states of the strongly interacting states with high filling fractions chosen via the parameters of the coupling. We study the coherent dynamics of this process in one dimension (1D) using a modified form of the time-evolving block decimation (TEBD) algorithm, and obtain crystalline states for system sizes and parameters corresponding to realistic experimental configurations. For polar molecules these crystalline states will be long-lived, assisting in a characterization of the state via the measurement of correlation functions. We also show that as the coupling strength increases in the model, the crystalline order is broken. This is characterized in 1D by a change in density-density correlation functions, which decay to a constant in the crystalline regime, but show different regions of exponential and algebraic decay for larger coupling strengths.

cond-mat.quant-gas↗

arXiv2011

Atomic matter-wave revivals with definite atom number in an optical lattice

We study the collapse and revival of interference patterns in the momentum distribution of atoms in optical lattices, using a projection technique to properly account for the fixed total number of atoms in the system. We consider the common experimental situation in which weakly interacting bosons are loaded into a shallow lattice, which is suddenly made deep. The collapse and revival of peaks in the momentum distribution is then driven by interactions in a lattice with essentially no tunnelling. The projection technique allows to us to treat inhomogeneous (trapped) systems exactly in the case that non-interacting bosons are loaded into the system initially, and we use time-dependent density matrix renormalization group techniques to study the system in the case of finite tunnelling in the lattice and finite initial interactions. For systems of more than a few sites and particles, we find good agreement with results calculated via a naive approach, in which the state at each lattice site is described by a coherent state in the particle occupation number. However, for systems on the order of 10 lattice sites, we find experimentally measurable discrepancies to the results predicted by this standard approach.

cond-mat.quant-gas↗

arXiv2010

Dissipation-induced d-Wave Pairing of Fermionic Atoms in an Optical Lattice

We show how dissipative dynamics can give rise to pairing for two-component fermions on a lattice. In particular, we construct a "parent" Liouvillian operator so that a BCS-type state of a given symmetry, e.g. a d-wave state, is reached for arbitrary initial states in the absence of conservative forces. The system-bath couplings describe single-particle, number conserving and quasi-local processes. The pairing mechanism crucially relies on Fermi statistics. We show how such Liouvillians can be realized via reservoir engineering with cold atoms representing a driven dissipative dynamics.

cond-mat.quant-gas↗

arXiv2010

Non-equilibrium dynamics of bosonic atoms in optical lattices: Decoherence of many-body states due to spontaneous emission

We analyze in detail the heating of bosonic atoms in an optical lattice due to incoherent scattering of light from the lasers forming the lattice. Because atoms scattered into higher bands do not thermalize on the timescale of typical experiments, this process cannot be described by the total energy increase in the system alone (which is determined by single-particle effects). The heating instead involves an important interplay between the atomic physics of the heating process and the many-body physics of the state. We characterize the effects on many-body states for various system parameters, where we observe important differences in the heating for strongly and weakly interacting regimes, as well as a strong dependence on the sign of the laser detuning from the excited atomic state. We compute heating rates and changes to characteristic correlation functions based both on perturbation theory calculations, and a time-dependent calculation of the dissipative many-body dynamics. The latter is made possible for 1D systems by combining time-dependent density matrix renormalization group (t-DMRG) methods with quantum trajectory techniques.

cond-mat.quant-gas↗

arXiv2010

Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part I: Formal Developments

We develop a quantum field theoretical framework to analytically study the three-body constrained Bose-Hubbard model beyond mean field and non-interacting spin wave approximations. It is based on an exact mapping of the constrained model to a theory with two coupled bosonic degrees of freedom with polynomial interactions, which have a natural interpretation as single particles and two-particle states. The procedure can be seen as a proper quantization of the Gutzwiller mean field theory. The theory is conveniently evaluated in the framework of the quantum effective action, for which the usual symmetry principles are now supplemented with a ``constraint principle'' operative on short distances. We test the theory via investigation of scattering properties of few particles in the limit of vanishing density, and we address the complementary problem in the limit of maximum filling, where the low lying excitations are holes and di-holes on top of the constraint induced insulator. This is the first of a sequence of two papers. The application of the formalism to the many-body problem, which can be realized with atoms in optical lattices with strong three-body loss, is performed in a related work [14].

cond-mat.quant-gas↗

arXiv2010

Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part II: Application to the Many-Body Problem

We analyze the ground state phase diagram of attractive lattice bosons, which are stabilized by a three-body onsite hardcore constraint. A salient feature of this model is an Ising type transition from a conventional atomic superfluid to a dimer superfluid with vanishing atomic condensate. The study builds on an exact mapping of the constrained model to a theory of coupled bosons with polynomial interactions, proposed in a related paper [11]. In this framework, we focus by analytical means on aspects of the phase diagram which are intimately connected to interactions, and are thus not accessible in a mean field plus spin wave approach. First, we determine shifts in the mean field phase border, which are most pronounced in the low density regime. Second, the investigation of the strong coupling limit reveals the existence of a new collective mode, which emerges as a consequence of enhanced symmetries in this regime. Third, we show that the Ising type phase transition, driven first order via the competition of long wavelength modes at generic fillings, terminates into a true Ising quantum critical point in the vicinity of half filling.

cond-mat.quant-gas↗

arXiv2010

Stabilization of the p-wave superfluid state in an optical lattice

It is hard to stabilize the p-wave superfluid state of cold atomic gas in free space due to inelastic collisional losses. We consider the p-wave Feshbach resonance in an optical lattice, and show that it is possible to have a stable p-wave superfluid state where the multi-atom collisional loss is suppressed through the quantum Zeno effect. We derive the effective Hamiltonian for this system, and calculate its phase diagram in a one-dimensional optical lattice. The results show rich phase transitions between the p-wave superfluid state and different types of insulator states induced either by interaction or by dissipation.

cond-mat.quant-gas↗

arXiv2010

Observability of Quantum Criticality and a Continuous Supersolid in Atomic Gases

We analyze the Bose-Hubbard model with a three-body hardcore constraint by mapping the system to a theory of two coupled bosonic degrees of freedom. We find striking features that could be observable in experiments, including a quantum Ising critical point on the transition from atomic to dimer superfluidity at unit filling, and a continuous supersolid phase for strongly bound dimers.

cond-mat.quant-gas↗

arXiv2009

A single trapped atom in front of an oscillating mirror

We investigate the Wigner-Weisskopf decay of a two level atom in front of an oscillating mirror. This work builds on and extends previous theoretical and experimental studies of the effects of a static mirror on spontaneous decay and resonance fluorescence. The spontaneously emitted field is inherently non-stationary due to the time-dependent boundary conditions and in order to study its spectral distribution we employ the operational definition of the spectrum of non-stationary light due to the seminal work by Eberly and Wodkiewicz. We find a rich dependence of this spectrum as well as of the effective decay rates and level shifts on the mirror-atom distance and on the amplitude and frequency of oscillations of the mirror. The results presented here provide the basis for future studies of more complex setups, where the motion of the atom and/or the mirror are included as quantum degrees of freedom.

quant-ph↗

arXiv2009

An atomic colour superfluid via three-body loss

Large three-body losses in a three-component Fermi gas confined in an optical lattice can prevent the occupation of a lattice site by three atoms. This effective constraint not only gives rise to a suppression of actual three-body loss, but stabilises BCS pairing phases by suppressing the formation of trions. We study the effects of the constraint using bosonisation and density matrix renormalisation group techniques (DMRG). We discuss the case of lithium experiments, and study the dissipative dynamics including loss using time-dependent DMRG with quantum trajectories methods.

cond-mat.quant-gas↗

arXiv2008

Atomic three-body loss as a dynamical three-body interaction

We discuss how large three-body loss of atoms in an optical lattice can give rise to effective hard-core three-body interactions. For bosons, in addition to the usual atomic superfluid, a dimer superfluid can then be observed for attractive two-body interactions. The non-equilibrium dynamics of preparation and stability of these phases are studied in 1D by combining time-dependent Density Matrix Renormalisation Group techniques with a quantum trajectories method.

cond-mat.other↗

arXiv2008

Physical replicas and the Bose-glass in cold atomic gases

We study cold atomic gases in a disorder potential and analyze the correlations between different systems subjected to the same disorder landscape. Such independent copies with the same disorder landscape are known as replicas. While in general these are not accessible experimentally in condensed matter systems, they can be realized using standard tools for controlling cold atomic gases in an optical lattice. Of special interest is the overlap function which represents a natural order parameter for disordered systems and is a correlation function between the atoms of two independent replicas with the same disorder. We demonstrate an efficient measurement scheme for the determination of this disorder-induced correlation function. As an application, we focus on the disordered Bose-Hubbard model and determine the overlap function within perturbation theory and a numerical analysis. We find that the measurement of the overlap function allows for the identification of the Bose-glass phase in certain parameter regimes.

cond-mat.other↗

arXiv2008

State-dependent, addressable subwavelength lattices with cold atoms

We discuss how adiabatic potentials can be used to create addressable lattices on a subwavelength scale, which can be used as a tool for local operations and readout within a lattice substructure, while taking advantage of the faster timescales and higher energy and temperature scales determined by the shorter lattice spacing. For alkaline-earth-like atoms with non-zero nuclear spin, these potentials can be made state dependent, for which we give specific examples with $^{171}$Yb atoms. We discuss in detail the limitations in generating the lattice potentials, in particular non-adiabatic losses, and show that the loss rates can always be made exponentially small by increasing the laser power.

cond-mat.other↗

arXiv2007

Andreev-like reflections with cold atoms

We propose a setup in which Andreev-like reflections predicted for 1D transport systems could be observed time-dependently using cold atoms in a 1D optical lattice. Using time-dependent Density Matrix Renormalisation Group methods we analyse the wavepacket dynamics as a density excitation propagates across a boundary in the interaction strength. These phenomena exhibit good correspondence with predictions from Luttinger liquid models and could be observed in current experiments in the context of the Bose-Hubbard model.

cond-mat.other↗

arXiv2007

Atomic lattice excitons: from condensates to crystals

We discuss atomic lattice excitons (ALEs), bound particle-hole pairs formed by fermionic atoms in two bands of an optical lattice. Such a system provides a clean setup to study fundamental properties of excitons, ranging from condensation to exciton crystals (which appear for a large effective mass ratio between particles and holes). Using both mean-field treatments and 1D numerical computation, we discuss the properities of ALEs under varying conditions, and discuss in particular their preparation and measurement.

cond-mat.other↗

arXiv2006

Dissipative dynamics of atomic Hubbard models coupled to a phonon bath: Dark state cooling of atoms within a Bloch band of an optical lattice

We analyse a laser assisted sympathetic cooling scheme for atoms within the lowest Bloch band of an optical lattice. This scheme borrows ideas from sub-recoil laser cooling, implementing them in a new context in which the atoms in the lattice are coupled to a BEC reservoir. In this scheme, excitation of atoms between Bloch bands replaces the internal structure of atoms in normal laser cooling, and spontaneous emission of photons is replaced by creation of excitations in the BEC reservoir. We analyse the cooling process for many bosons and fermions, and obtain possible temperatures corresponding to a small fraction of the Bloch band width within our model. This system can be seen as a novel realisation of a many-body open quantum system.

cond-mat.other↗