261 research outputs found
Creation of resilient entangled states and a resource for measurement-based quantum computation with optical superlattices
We investigate how to create entangled states of ultracold atoms trapped in
optical lattices by dynamically manipulating the shape of the lattice
potential. We consider an additional potential (the superlattice) that allows
both the splitting of each site into a double well potential, and the control
of the height of potential barrier between sites. We use superlattice
manipulations to perform entangling operations between neighbouring qubits
encoded on the Zeeman levels of the atoms without having to perform transfers
between the different vibrational states of the atoms. We show how to use
superlattices to engineer many-body entangled states resilient to collective
dephasing noise. Also, we present a method to realize a 2D resource for
measurement-based quantum computing via Bell-pair measurements. We analyze
measurement networks that allow the execution of quantum algorithms while
maintaining the resilience properties of the system throughout the computation.Comment: 23 pages, 6 figures, IOP style, published in New Journal of Physics.
Minor corrections/few typos remove
Cooling in the single-photon strong-coupling regime of cavity optomechanics
In this paper we discuss how red-sideband cooling is modified in the
single-photon strong-coupling regime of cavity optomechanics where the
radiation pressure of a single photon displaces the mechanical oscillator by
more than its zero-point uncertainty. Using Fermi's Golden rule we calculate
the transition rates induced by the optical drive without linearizing the
optomechanical interaction. In the resolved-sideband limit we find
multiple-phonon cooling resonances for strong single-photon coupling that lead
to non-thermal steady states including the possibility of phonon anti-bunching.
Our study generalizes the standard linear cooling theory.Comment: 4 pages, 3 figure
Proposal for entangling remote micromechanical oscillators via optical measurements
We propose an experiment to create and verify entanglement between remote
mechanical objects by use of an optomechanical interferometer. Two optical
cavities, each coupled to a separate mechanical oscillator, are coherently
driven such that the oscillators are laser cooled to the quantum regime. The
entanglement is induced by optical measurement and comes about by combining the
output from the two cavities to erase which-path information. It can be
verified through measurements of degrees of second-order coherence of the
optical output field. The experiment is feasible in the regime of weak
optomechanical coupling. Realistic parameters for the membrane-in-the-middle
geometry suggest entangled state lifetimes on the order of milliseconds.Comment: 4 pages, 2 figures + supplementary material (7 pages, 2 figs).
Updates in v2: New Eq. (7) and Fig. 1 - results unchanged. Added
supplementary material with various details. Updates in v3: Minor changes,
journal ref. adde
Quantum-limited amplification and parametric instability in the reversed dissipation regime of cavity optomechanics
Cavity optomechanical phenomena, such as cooling, amplification or
optomechanically induced transparency, emerge due to a strong imbalance in the
dissipation rates of the parametrically coupled electromagnetic and mechanical
resonators. Here we analyze the reversed dissipation regime where the
mechanical energy relaxation rate exceeds the energy decay rate of the
electromagnetic cavity. We demonstrate that this regime allows for
mechanically-induced amplification (or cooling) of the electromagnetic mode.
Gain, bandwidth, and added noise of this electromagnetic amplifier are derived
and compared to amplification in the normal dissipation regime. In addition, we
analyze the parametric instability, i.e. optomechanical Brillouin lasing, and
contrast it to conventional optomechanical phonon lasing. Finally, we propose
an experimental scheme that realizes the reversed dissipation regime using
parametric coupling and optomechanical cooling with a second electromagnetic
mode enabling quantum-limited amplification. Recent advances in high-Q
superconducting microwave resonators make the reversed dissipation regime
experimentally realizable.Comment: 5+3 pages, 5 figures, 1 tabl
Floquet approach to bichromatically driven cavity-optomechanical systems
We develop a Floquet approach to solve time-periodic quantum Langevin
equations in steady state. We show that two-time correlation functions of
system operators can be expanded in a Fourier series and that a generalized
Wiener-Khinchin theorem relates the Fourier transform of their zeroth Fourier
component to the measured spectrum. We apply our framework to bichromatically
driven cavity optomechanical systems, a setting in which mechanical oscillators
have recently been prepared in quantum-squeezed states. Our method provides an
intuitive way to calculate the power spectral densities for time-periodic
quantum Langevin equations in arbitrary rotating frames.A.N. holds a University Research Fellowship from the Royal Society and acknowledges additional support from the Winton Programme for the Physics of Sustainability. D.M. acknowledges support by the UK Engineering and Physical Sciences Research Council (EPSRC) under Grant No. EP/M506485/1.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevA.94.02380
Optomechanical dual-beam backaction-evading measurement beyond the rotating-wave approximation
We present the exact analytical solution of the explicitly time-periodic quantum Langevin equation describing the dual-beam backaction-evading measurement of a single mechanical oscillator quadrature due to V. B. Braginsky, Y. I. Vorontsov, and K. S. Thorne [Science 209, 547 (1980)] beyond the commonly used rotating-wave approximation. We show that counterrotating terms lead to extra sidebands in the optical and mechanical spectra and to a modification of the main peak. Physically, the backaction of the measurement is due to periodic coupling of the mechanical resonator to a light-field quadrature that only contains cavity-filtered shot noise. Since this fact is independent of other degrees of freedom the resonator might be coupled to, our solution can be generalized, including to dissipatively or parametrically squeezed oscillators, as well as recent two-mode backaction-evading measurements.Royal Society (University Research Fellowship), Winton Programme for the Physics of Sustainabilit
Emergence of continuous rotational symmetries in ultracold atoms coupled to optical cavities
We investigate the physics of a gas of ultracold atoms coupled to three
single-mode optical cavities and transversely pumped with a laser. Recent work
has demonstrated that, for two cavities, the symmetries of
each cavity can be combined into a global symmetry. Here, we show that
when adding an extra cavity mode, the low-energy description of this system can
additionally exhibit an rotational symmetry which can be spontaneously
broken. This leads to a superradiant phase transition in all the cavities
simultaneously, and the appearance of Goldstone and amplitude modes in the
excitation spectrum. We determine the phase diagram of the system, which shows
the emergence and breaking of the continuous symmetries and displays first- and
second-order phase transitions. We also obtain the excitation spectrum for each
phase and discuss the atomic self-organized structures that emerge in the
different superradiant phases. We argue that coupling the atoms equally to
different modes will in general generate a global symmetry if the mode
frequencies can be tuned to the same value
Current rectification in a double quantum dot through fermionic reservoir engineering
Reservoir engineering is a powerful tool for the robust generation of quantum
states or transport properties. Using both a weak-coupling quantum master
equation and the exact solution, we show that directional transport of
electrons through a double quantum dot can be achieved through an appropriately
designed electronic environment. Directionality is attained through the
interference of coherent and dissipative coupling. The relative phase is tuned
with an external magnetic field, such that directionality can be reversed, as
well as turned on and off dynamically. Our work introduces fermionic reservoir
engineering, paving the way to a new class of nanoelectronic devices
Dynamical generation of synthetic electric fields for photons in the quantum regime
Optomechanics offers a natural way to implement synthetic dynamical gauge
fields, leading to synthetic electric fields for phonons and, as a consequence,
to unidirectional light transport. Here we investigate the quantum dynamics of
synthetic gauge fields in the minimal setup of two optical modes coupled by
phonon-assisted tunneling where the phonon mode is undergoing
self-oscillations. We use the quantum van-der-Pol oscillator as the simplest
dynamical model for a mechanical self-oscillator that allows us to perform
quantum master equation simulations. We identify a single parameter, which
controls the strength of quantum fluctuations, enabling us to investigate the
classical-to-quantum crossover. We show that the generation of synthetic
electric fields is robust against noise and that it leads to unidirectional
transport of photons also in the quantum regime, albeit with a reduced
isolation ratio. Our study opens the path for studying dynamical gauge fields
in the quantum regime based on optomechanical arrays
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