Heating rates for an atom in a far-detuned optical lattice

We calculate single atom heating rates in a far detuned optical lattice, in connection with recent experiments. We first derive a master equation, including a realistic atomic internal structure and a quantum treatment of the atomic motion in the lattice. The experimental feature that optical lattices are obtained by superimposing laser standing waves of different frequencies is also included, which leads to a micromotional correction to the light shift that we evaluate. We then calculate, and compare to experimental results, two heating rates, the "total" heating rate (corresponding to the increase of the total mechanical energy of the atom in the lattice), and the ground bande heating rate (corresponding to the increase of energy within the ground energy band of the lattice).Comment: 11 pages, 3 figures, 1 tabl

Resonances for a Hydrogenic System or a Harmonic Oscillator Strongly Coupled to a Field

We calculate resonances which are formed by a particle in a potential which is either Coulombian or quadratic when the particle is strongly coupled to a massless boson, taking only two energy levels into consideration. From these calculations we derive how the moving away of the particle from its attraction center goes together with the energy lowering of hybrid states that this particle forms with the field. We study the width of these states and we show that stable states may also appear in the coupling.Comment: 17 pages, 6 figure

Decays in Quantum Hierarchical Models

We study the dynamics of a simple model for quantum decay, where a single state is coupled to a set of discrete states, the pseudo continuum, each coupled to a real continuum of states. We find that for constant matrix elements between the single state and the pseudo continuum the decay occurs via one state in a certain region of the parameters, involving the Dicke and quantum Zeno effects. When the matrix elements are random several cases are identified. For a pseudo continuum with small bandwidth there are weakly damped oscillations in the probability to be in the initial single state. For intermediate bandwidth one finds mesoscopic fluctuations in the probability with amplitude inversely proportional to the square root of the volume of the pseudo continuum space. They last for a long time compared to the non-random case

Nonlinear Faraday Rotation and Superposition-State Detection in Cold Atoms

We report on the first observation of nonlinear Faraday rotation with cold atoms at a temperature of ~100 uK. The observed nonlinear rotation of the light polarization plane is up to 0.1 rad over the 1 mm size atomic cloud in approximately 10 mG magnetic field. The nonlinearity of rotation results from long-lived coherence of ground-state Zeeman sublevels created by a near-resonant light. The method allows for creation, detection and control of atomic superposition states. It also allows applications for precision magnetometry with high spatial and temporal resolution.Comment: 5 pages, 6 figure

Decoherence and dephasing in strongly driven colliding Bose-Einstein condensates

We report on a series of measurements of decoherence and wavepacket dephasing between two colliding, strongly coupled, identical Bose-Einstein condensates. We measure, in the strong excitation regime, a suppression of the mean-field shift, compared to the shift which is observed for a weak excitation. This suppression is explained by applying the Gross-Pitaevskii energy functional. By selectively counting only the non-decohered fraction in a time of flight image we observe oscillations for which both inhomogeneous and Doppler broadening are suppressed, in quantitative agreement with a full Gross-Pitaevskii equation simulation. If no post selection is used, the decoherence rate due to collisions can be extracted, and is in agreement with the local density average calculated rate.Comment: 4 pages, 5 figure

Entanglement swapping between spacelike separated atoms

We show a mechanism that projects a pair of neutral two-level atoms from an initially uncorrelated state to a maximally entangled state while they remain spacelike separated. The atoms begin both excited in a common electromagnetic vacuum, and the radiation is collected with a partial Bell-state analyzer. If the interaction time is short enough and a certain two-photon Bell state is detected after the interaction, a high degree of entanglement, even maximal, can be generated while one atom is outside the light cone of the other, for arbitrary large interatomic distances.Comment: v2: version accepted in Phys. Rev.

Narrow band microwave radiation from a biased single-Cooper-pair transistor

We show that a single-Cooper-pair transistor (SCPT) electrometer emits narrow-band microwave radiation when biased in its sub-gap region. Photo activation of quasiparticle tunneling in a nearby SCPT is used to spectroscopically detect this radiation, in a configuration that closely mimics a qubit-electrometer integrated circuit. We identify emission lines due to Josephson radiation and radiative transport processes in the electrometer, and argue that a dissipative superconducting electrometer can severely disrupt the system it attempts to measure.Comment: 4 pages, 3 figure

Entanglement, identical particles and the uncertainty principle

A new uncertainty relation (UR) is obtained for a system of N identical pure entangled particles if we use symmetrized observables when deriving the inequality. This new expression can be written in a form where we identify a term which explicitly shows the quantum correlations among the particles that constitute the system. For the particular cases of two and three particles, making use of the Schwarz inequality, we obtain new lower bounds for the UR that are different from the standard one.Comment: 5 pages, no figure; v2: title, abstract, and focus slightly changed; a couple of sections rewritten and a new one added; published versio

Atom Lithography with Near-Resonant Light Masks: Quantum Optimization Analysis

We study the optimal focusing of two-level atoms with a near resonant standing wave light, using both classical and quantum treatments of the problem. Operation of the focusing setup is considered as a nonlinear spatial squeezing of atoms in the thin- and thick-lens regimes. It is found that the near-resonant standing wave focuses the atoms with a reduced background in comparison with far-detuned light fields. For some parameters, the quantum atomic distribution shows even better localization than the classical one. Spontaneous emission effects are included via the technique of quantum Monte Carlo wave function simulations. We investigate the extent to which non-adiabatic and spontaneous emission effects limit the achievable minimal size of the deposited structures.Comment: 10 pages including 11 figures in Revte

Slow quench dynamics of periodically driven quantum gases

We study the evolution of bosons in a periodically driven optical lattice during a slow change of the driving amplitude. Both the regime of high frequency and low frequency driving are investigated. In the low frequency regime, resonant absorption of energy is observed. In the high frequency regime, the dynamics is compared to a system with an effective Hamiltonian in which the atoms are `dressed' by the driving field. This `dressing' can dramatically change the amplitude and sign of the effective tunneling. A particular focus of this study is the investigation of the time-scales necessary for the evolving quantum state to follow almost adiabatically to the ground-state of the effective many body system.Comment: 10 pages, 8 figure