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M. G. Moore

Publications and source records attributed to M. G. Moore.

At least 19 recordsLinked to original sources
arXiv2011

Robust sub-shot-noise measurement via Rabi-Josephson oscillations in bimodal Bose-Einstein condensates

Mach-Zehnder atom interferometry requires hold-time phase-squeezing to attain readout accuracy below the standard quantum limit. This increases its sensitivity to phase-diffusion, restoring shot-noise scaling of the optimal signal-to-noise ratio, $s_o$, in the presence of interactions. The contradiction between the preparations required for readout accuracy and robustness to interactions, is removed by monitoring Rabi-Josephson oscillations instead of relative-phase oscillations during signal acquisition. Optimizing $s_o$ with a Gaussian squeezed input, we find that hold-time number squeezing satisfies both demands and that sub-shot-noise scaling is retained even for strong interactions.

cond-mat.quant-gas↗
arXiv2009

Ultra-bright omni-directional collective emission of correlated photon pairs from atomic vapors

Spontaneous four-wave mixing can generate highly correlated photon pairs from atomic vapors. We show that multi-photon pumping of dipole-forbidden transitions in a recoil-free geometry can result in ultra-bright pair-emission in the full 4πsolid angle, while strongly suppresses background Rayleigh scattering and associated atomic heating, Such a system can produce photon pairs at rates of ~ 10 ^12 per second, given only moderate optical depths of 10 ~ 100, or alternatively, the system can generate paired photons with sub-natural bandwidths at lower production rates. We derive a rate-equation based theory of the collective atomic population and coherence dynamics, and present numerical simulations for a toy model, as well as realistic model systems based on 133 Cs and 171 Yb level structures. Lastly, we demonstrate that dark-state adiabatic following (EIT) and/or timescale hierarchy protects the paired photons from reabsorption as they propagate through an optically thick sample.

physics.atom-ph↗
arXiv2009

Ultra-bright biphoton emission from an atomic vapor based on Doppler-free four-wave-mixing and collective emission

We propose a novel `butterfly' level scheme to generate highly correlated photon pairs from atomic vapors. With multi-photon Doppler-free pumping, background Rayleigh scattering is dipole-forbidden and collective emission is permitted in all directions. This results in usable pairs generated simultaneously in the full $4π$ solid angle. Collecting these pairs can produce photon pairs at a rate of $\sim 10^{12}$ per second, given only moderate ensemble sizes of $\sim 10^6$ atoms.

quant-ph↗
arXiv2008

Zeno Quantum Gates in Semiconductor Quantum Dots

We propose a scheme for a two-qubit conditional phase gate by quantum Zeno effect with semiconductor quantum dots. The system consists of two charged dots and one ancillary dot that can perform Rabi oscillations under a resonant laser pulse. The quantum Zeno effect is induced by phonon-assisted exciton relaxation between the ancillary dot and the charged dots, which is equivalent to a continuous measurement. We solve analytically the master equation and simulate the dynamics of the system using a realistic set of parameters. In contrast to standard schemes, larger phonon relaxation rates increase the fidelity of the operations.

cond-mat.other↗
arXiv2008

On-demand generation of entanglement of atomic qubits via optical interferometry

The problem of on-demand generation of entanglement between single-atom qubits via a common photonic channel is examined within the framework of optical interferometry. As expected, for a Mach-Zehnder interferometer with coherent laser beam as input, a high-finesse optical cavity is required to overcome sensitivity to spontaneous emission. We show, however, that with a twin-Fock input, useful entanglement can in principle be created without cavity-enhancement. Both approaches require single-photon resolving detectors, and best results would be obtained by combining both cavity-feedback and twin-Fock inputs. Such an approach may allow a fidelity of $.99$ using a two-photon input and currently available mirror and detector technology. In addition, we study interferometers based on NOON states and show that they perform similarly to the twin-Fock states, yet without the need for high-precision photo-detectors. The present interferometrical approach can serve as a universal, scalable circuit element for quantum information processing, from which fast quantum gates, deterministic teleportation, entanglement swapping $etc.$, can be realized with the aid of single-qubit operations.

quant-ph↗
arXiv2008

Optimized Double-well quantum interferometry with Gaussian squeezed-states

A Mach-Zender interferometer with a gaussian number-difference squeezed input state can exhibit sub-shot-noise phase resolution over a large phase-interval. We obtain the optimal level of squeezing for a given phase-interval $Δθ_0$ and particle number $N$, with the resulting phase-estimation uncertainty smoothly approaching $3.5/N$ as $Δθ_0$ approaches 10/N, achieved with highly squeezed states near the Fock regime. We then analyze an adaptive measurement scheme which allows any phase on $(-π/2,π/2)$ to be measured with a precision of $3.5/N$ requiring only a few measurements, even for very large $N$. We obtain an asymptotic scaling law of $Δθ\approx (2.1+3.2\ln(\ln(N_{tot}\tanΔθ_0)))/N_{tot}$, resulting in a final precision of $\approx 10/N_{tot}$. This scheme can be readily implemented in a double-well Bose-Einstein condensate system, as the optimal input states can be obtained by adiabatic manipulation of the double-well ground state.

quant-ph↗
arXiv2006

Long-distance teleportation of atomic qubit via optical interferometry

The problem of long-distance teleportation of single-atom qubits via a common photonic channel is examined within the framework of a Mach-Zender optical interferometer. As expected, when a coherent state is used as input, a high-finesse optical cavity is required to overcome sensitivity to spontaneous emission. However, we find that a number-squeezed light field in a twin-Fock state can in principle create useful entanglement without cavity-enhancement. Both approaches require single photon counting detectors, and best results are obtained by combining cavity-feedback with twin-fock inputs. Such an approach may allow a fidelity of $.99$ using a two-photon input and currently available mirror and detector technology. In addition, the present approach can be conveniently extended to generate multi-site entanglement and entanglement swapping, both of which are necessities in quantum networks.

quant-ph↗
arXiv2005

Creation, detection and decoherence of Schrodinger cat states in Bose-Einstein condensates

We study the possibility to create many-particle Schrödinger cat-like states by using a Feshbach resonance to reverse the sign of the scattering length of a Bose-Einstein condensate trapped in a double-well potential. To address the issue of experimental verification of coherence in the cat-like state, we study the revival of the initial condensate state in the presence of environmentally-induced decoherence. As a source of decoherence, we consider the interaction between the atoms and the electromagnetic vacuum, due to the polarization induced by an incident laser field. We find that the resulting decoherence is directly related to the rate at which spontaneously scattered photons carry away sufficient information to distinguish between the two atom-distributions which make-up the cat state. We show that for a 'perfect' cat-state, a single scattered photon will bring about a collapse of the superposition, while a less-than-perfect cat-like state can survive multiple scatterings before collapse occurs. In addition, we study the dephasing effect of atom-atom collisions on the cat-like states.

cond-mat.other↗
arXiv2005

A pseudo-potential analog for zero-range photoassociation and Feshbach resonance

A zero-range approach to atom-molecule coupling is developed in analogy to the Fermi-Huang pseudo-potential treatment of atom-atom interactions. It is shown by explicit comparison to an exactly-solvable finite-range model that replacing the molecular bound-state wavefunction with a regularized delta-function can reproduce the exact scattering amplitude in the long-wavelength limit. Using this approach we find an analytical solution to the two-channel Feshbach resonance problem for two atoms in a spherical harmonic trap.

cond-mat.other↗
arXiv2004

Scattering in tight atom waveguides

Using the Theory of Scattering in Restricted Geometries developed by A. Lupu-Sax as a starting point, we present a comprehensive multi-channel theory of atom-atom scattering in tight atom waveguides.

cond-mat.other↗
arXiv2003

Atom-Atom Scattering Under Cylindrical Harmonic Confinement: Numerical and Analytical Studies of the Confinement Induced Resonance

In a recent article [M. Olshanii, Phys. Rev. Lett. {\bf 81}, 938 (1998)], an analytic solution of atom-atom scattering with a delta-function pseudopotential interaction in the presence of transverse harmonic confinement yielded an effective coupling constant that diverged at a `confinement induced resonance.' In the present work, we report numerical results that corroborate this resonance for more realistic model potentials. In addition, we extend the previous theoretical discussion to include two-atom bound states in the presence of transverse confinement, for which we also report numerical results here

cond-mat↗
arXiv2002

Controlling two-species Mott-insulator phses in an optical lattice to form an array of dipolar molecules

We consider the transfer of a two-species Bose-Einstein condensate into an optical lattice with a density such that that a Mott-insulator state with one atom per species per lattice site is obtained in the deep lattice regime. Depending on collision parameters the result could be either a `mixed' or a `separated' Mott-insulator phase. Such a `mixed' two-species insulator could then be photo-associated into an array of dipolar molecules suitable for quantum computation or the formation of a dipolar molecular condensate. For the case of a $^{87}$Rb-$^{41}$K two-species BEC, however, the large inter-species scattering length makes obtaining the desired `mixed' Mott insulator phase difficult. To overcome this difficulty we investigate the effect of varying the lattice frequency on the mean-field interaction and find a favorable parameter regime under which a lattice of dipolar molecules could be generated.

cond-mat↗
arXiv2002

Directional `superradiant' collisions: bosonic amplification of atom pairs emitted from an elongated Bose-Einstein condensate

We study spontaneous directionality in the bosonic amplification of atom pairs emitted from an elongated Bose-Einstein condensate (BEC), an effect analogous to `superradiant' emission of atom-photon pairs. Using a simplified model, we make analytic predictions regarding directional effects for both atom-atom and atom-photon emission. These are confirmed by numerical mean-field simulations, demonstrating the the feasibility of nearly perfect directional emission along the condensate axis. The dependence of the emission angle on the pump strength for atom-atom pairs is significantly different than for atom-photon pairs.

cond-mat↗
arXiv2002

Bose-enhanced chemistry: Amplification of selectivity in the dissociation of molecular Bose-Einstein condensates

We study the photodissociation chemistry of a quantum degenerate gas of bosonic triatomic $ABC$ molecules, assuming two open rearrangement channels ($AB+C$ or $A+BC$). The equations of motion are equivalent to those of a parametric multimode laser, resulting in an exponential buildup of macroscopic mode populations. By exponentially amplifying a small differential in the single-particle rate-coefficients, Bose stimulation leads to a nearly complete selectivity of the collective $N$-body process, indicating a novel type of ultra-selective quantum degenerate chemistry.

cond-mat↗
arXiv2000

Gravity-induced Wannier-Stark ladder in an optical lattice

We discuss the dynamics of ultracold atoms in an optical potential accelerated by gravity. The positions and widths of the Wannier-Stark ladder of resonances are obtained as metastable states. The metastable Wannier-Bloch states oscillate in a single band with the Bloch period. The width of the resonance gives the rate transition to the continuum.

cond-mat↗
arXiv2000

Atomic four-wave mixing: fermions versus bosons

We compare the efficiency of four-wave mixing in quantum degenerate gases of bosonic and fermionic atoms. It is shown that matter-wave gratings formed from either bosonic or fermionic atoms can in principle exhibit nearly identical Bragg-scattering, i.e. four-wave mixing, properties. This implies that effects such as coherent matter-wave amplification and superradiance can occur in degenerate fermi gases. While in the boson case the Bragg resonance is clearly due to `Bose enhancement', in the case of fermions the resonance is due to constructive many-particle quantum interference.

cond-mat↗
arXiv2000

Instabilities and self-socillations in atomic four-wave mixing

The development of integrated, waveguide-based atom optical devices requires a thorough understanding of nonlinear matter-wave mixing processes in confined geometries. This paper analyzes the stability of counterpropagating two-component Bose-Einstein condensates in such a geometry. The steady state field equations of this system are solved analytically, predicting a multivalued relation between the input and output field intensities. The spatio-temporal linear stability of these solutions is investigated numerically, leading to the prediction of a self-oscillation threshold that can be expressed in terms of a matter-wave analog of the Fresnel number in optics.

cond-mat↗