961 research outputs found
Measurement-Induced Long-Distance Entanglement of Superconducting Qubits using Optomechanical Transducers
Although superconducting systems provide a promising platform for quantum
computing, their networking poses a challenge as they cannot be interfaced to
light---the medium used to send quantum signals through channels at room
temperature. We show that mechanical oscillators can mediated such coupling and
light can be used to measure the joint state of two distant qubits. The
measurement provides information on the total spin of the two qubits such that
entangled qubit states can be postselected. Entanglement generation is possible
without ground-state cooling of the mechanical oscillators for systems with
optomechanical cooperativity moderately larger than unity; in addition, our
setup tolerates a substantial transmission loss. The approach is scalable to
generation of multipartite entanglement and represents a crucial step towards
quantum networks with superconducting circuits.Comment: Updated figures, close to published versio
Synchronization of Active Atomic Clocks via Quantum and Classical Channels
Superradiant lasers based on atomic ensembles exhibiting ultra-narrow optical
transitions can emit light of unprecedented spectral purity and may serve as
active atomic clocks. We consider two frequency-detuned active atomic clocks,
which are coupled in a cascaded setup, i.e. as master & slave lasers, and study
the synchronization of the slave to the master clock. In a setup where both
atomic ensembles are coupled to a common cavity mode such synchronization
phenomena have been predicted by Xu et al. [Phys. Rev. Lett. 113, 154101
(2014)] and experimentally observed by Weiner et al. [arXiv:1503.06464 (2015)].
Here we demonstrate that synchronization still occurs in cascaded setups but
exhibits distinctly different phase diagrams. We study the characteristics of
synchronization in comparison to the case of coupling through a common cavity.
We also consider synchronization through a classical channel where light of the
master laser is measured phase sensitively and the slave laser is injection
locked by feedback and compare to the results achievable by coupling through
quantum channels.Comment: 13 pages, 12 figure
Sub-Poissonian Phonon Lasing in Three-Mode Optomechanics
We propose to use the resonant enhancement of the parametric instability in
an optomechanical system of two optical modes coupled to a mechanical
oscillator to prepare mechanical states with sub-Poissonian phonon statistics.
Strong single photon coupling is not required. The requirements regarding
sideband resolution, circulating cavity power and environmental temperature are
in reach with state of the art parameters of optomechanical crystals. Phonon
antibunching can be verfied in a Hanburry-Brown-Twiss measurement on the output
field of the optomechanical cavity.Comment: 6 pages, 4 figure
Optomechanical sensing of spontaneous wave-function collapse
Quantum experiments with nanomechanical oscillators are regarded as a testbed
for hypothetical modifications of the Schr\"{o}dinger equation, which predict a
breakdown of the superposition principle and induce classical behavior at the
macro-scale. It is generally believed that the sensitivity to these
unconventional effects grows with the mass of the mechanical quantum system.
Here we show that the opposite is the case for optomechanical systems in the
presence of generic noise sources, such as thermal and measurement noise. We
determine conditions for distinguishing these decoherence processes from
possible collapse-induced decoherence in continuous optomechanical force
measurements.Comment: 3 figures, revised version with extended supplemental materia
Spatially Adiabatic Frequency Conversion in Optoelectromechanical Arrays
Faithful conversion of quantum signals between microwave and optical
frequency domains is crucial for building quantum networks based on
superconducting circuits. Optoelectromechanical systems, in which microwave and
optical cavity modes are coupled to a common mechanical oscillator, are a
promising route towards this goal. In these systems, efficient, low-noise
conversion is possible using a mechanically dark mode of the fields but the
conversion bandwidth is limited to a fraction of the cavity linewidth. Here, we
show that an array of optoelectromechanical transducers can overcome this
limitation and reach a bandwidth that is larger than the cavity linewidth. The
coupling rates are varied in space throughout the array so that the
mechanically dark mode of the propagating fields adiabatically changes from
microwave to optical or vice versa. This strategy also leads to significantly
reduced thermal noise with the collective optomechanical cooperativity being
the relevant figure of merit. Finally, we demonstrate that, quite surprisingly,
the bandwidth enhancement per transducer element is largest for small arrays;
this feature makes our scheme particularly attractive for state-of-the-art
experimental setups.Comment: 18 pages, 10 figures (including Supplemental Material
High fidelity teleportation between light and atoms
We show how high fidelity quantum teleportation of light to atoms can be
achieved in the same setup as was used in the recent experiment [J. Sherson
et.al., quant-ph/0605095, accepted by Nature], where such an inter-species
quantum state transfer was demonstrated for the first time. Our improved
protocol takes advantage of the rich multimode entangled structure of the state
of atoms and scattered light and requires simple post-processing of homodyne
detection signals and squeezed light in order to achieve fidelities up to 90%
(85%) for teleportation of coherent (qubit) states under realistic experimental
conditions. The remaining limitation is due to atomic decoherence and light
losses.Comment: 5 pages, 3 figure
Light-Mediated Collective Atomic Motion in an Optical Lattice Coupled to a Membrane
We observe effects of collective atomic motion in a one-dimensional optical
lattice coupled to an optomechanical system. In this hybrid atom-optomechanical
system, the lattice light generates a coupling between the lattice atoms as
well as between atoms and a micromechanical membrane oscillator. For large atom
numbers we observe an instability in the coupled system, resulting in
large-amplitude atom-membrane oscillations. We show that this behavior can be
explained by light-mediated collective atomic motion in the lattice, which
arises for large atom number, small atom-light detuning and asymmetric pumping
of the lattice, in agreement with previous theoretical work. The model connects
the optomechanical instability to a phase delay in the global atomic
back-action onto the lattice light, which we observe in a direct measurement.Comment: new introduction, title and outlook; small modifications of the main
text and figure
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