84 research outputs found
Entanglement and spin-squeezing in a network of distant optical lattice clocks
We propose an approach for collective enhancement of precision for remotely
located optical lattice clocks and a way of generation of the
Einstein-Podolsky-Rosen state of remote clocks. Close to Heisenberg scaling of
the clock precision with the number of clocks M can be achieved even for an
optical channel connecting clocks with substantial losses. This scenario
utilizes a collective quantum nondemolition measurement on clocks with parallel
Bloch vectors for enhanced measurement precision. We provide an optimal network
solution for distant clocks as well as for clocks positioned in close proximity
of each other. In the second scenario, we employ collective dissipation to
drive two clocks with oppositely oriented Bloch vectors into a steady state
entanglement. The corresponding EPR entanglement provides enhanced time sharing
beyond the projection noise limit between the two quantum synchronized clocks
protected from eavesdropping, as well as allows better characterization of
systematic effects
Fock-state view of weak-value measurements and implementation with photons and atomic ensembles
Weak measurements in combination with post-selection can give rise to a
striking amplification effect (related to a large "weak value"). We show that
this effect can be understood by viewing the initial state of the pointer as
the ground state of a fictional harmonic oscillator, helping us to clarify the
transition from the weak-value regime to conventional dark-port interferometry.
We then describe how to implement fully quantum weak-value measurements
combining photons and atomic ensembles.Comment: 4 pages, 1 figur
Quantum cloning at the light-atoms interface: copying a coherent light state into two atomic quantum memories
A scheme for the optimal Gaussian cloning of coherent light states at the
light-atoms interface is proposed. The distinct feature of this proposal is
that the clones are stored in an atomic quantum memory, which is important for
applications in quantum communication. The atomic quantum cloning machine
requires only a single passage of the light pulse through the atomic ensembles
followed by the measurement of a light quadrature and an appropriate feedback,
which renders the protocol experimentally feasible. An alternative protocol,
where one of the clones is carried by the outgoing light pulse, is discussed in
connection with quantum key distribution.Comment: 4 pages, 3 figures, RevTeX
Phonon counting thermometry of an ultracoherent membrane resonator near its motional ground state
Generation of non-Gaussian quantum states of macroscopic mechanical objects
is key to a number of challenges in quantum information science, ranging from
fundamental tests of decoherence to quantum communication and sensing. Heralded
generation of single-phonon states of mechanical motion is an attractive way
towards this goal, as it is, in principle, not limited by the object size. Here
we demonstrate a technique which allows for generation and detection of a
quantum state of motion by phonon counting measurements near the ground state
of a 1.5 MHz micromechanical oscillator. We detect scattered photons from a
membrane-in-the-middle optomechanical system using an ultra-narrowband optical
filter, and perform Raman-ratio thermometry and second-order intensity
interferometry near the motional ground state ( phonons).
With an effective mass in the nanogram range, our system lends itself for
studies of long-lived non-Gaussian motional states with some of the heaviest
objects to date.Comment: 11 pages, 10 figure
Quantum Information at the Interface of Light with Atomic Ensembles and Micromechanical Oscillators
This article reviews recent research towards a universal light-matter
interface. Such an interface is an important prerequisite for long distance
quantum communication, entanglement assisted sensing and measurement, as well
as for scalable photonic quantum computation. We review the developments in
light-matter interfaces based on room temperature atomic vapors interacting
with propagating pulses via the Faraday effect. This interaction has long been
used as a tool for quantum nondemolition detections of atomic spins via light.
It was discovered recently that this type of light-matter interaction can
actually be tuned to realize more general dynamics, enabling better performance
of the light-matter interface as well as rendering tasks possible, which were
before thought to be impractical. This includes the realization of improved
entanglement assisted and backaction evading magnetometry approaching the
Quantum Cramer-Rao limit, quantum memory for squeezed states of light and the
dissipative generation of entanglement. A separate, but related, experiment on
entanglement assisted cold atom clock showing the Heisenberg scaling of
precision is described. We also review a possible interface between collective
atomic spins with nano- or micromechanical oscillators, providing a link
between atomic and solid state physics approaches towards quantum information
processing
Quantum Teleportation of Dynamics and Effective Interactions Between Remote Systems
Most protocols for Quantum Information Processing consist of a series of
quantum gates, which are applied sequentially. In contrast, interactions, for
example between matter and fields, as well as measurements such as homodyne
detection of light, are typically continuous in time. We show how the ability
to perform quantum operations continuously and deterministically can be
leveraged for inducing non-local dynamics between two separate parties. We
introduce a scheme for the engineering of an interaction between two remote
systems and present a protocol which induces a dynamics in one of the parties,
which is controlled by the other one. Both schemes apply to continuous variable
systems, run continuously in time and are based on real-time feedback
Long-lived non-classical correlations for scalable quantum repeaters at room temperature
Heralded single-photon sources with on-demand readout are promising
candidates for quantum repeaters enabling long-distance quantum communication.
The need for scalability of such systems requires simple experimental
solutions, thus favouring room-temperature systems. For quantum repeater
applications, long delays between heralding and single-photon readout are
crucial. Until now, this has been prevented in room-temperature atomic systems
by fast decoherence due to thermal motion. Here we demonstrate efficient
heralding and readout of single collective excitations created in warm caesium
vapour. Using the principle of motional averaging we achieve a collective
excitation lifetime of ms, two orders of magnitude larger than
previously achieved for single excitations in room-temperature sources. We
experimentally verify non-classicality of the light-matter correlations by
observing a violation of the Cauchy-Schwarz inequality with .
Through spectral and temporal analysis we identify intrinsic four-wave mixing
noise as the main contribution compromising single-photon operation of the
source.Comment: 21 pages total, the first 17 pages are the main article and the
remaining pages are supplemental materia
Heralded amplification for precision measurements with spin ensembles
We propose a simple heralded amplification scheme for small rotations of the
collective spin of an ensemble of particles. Our protocol makes use of two
basic primitives for quantum memories, namely partial mapping of light onto an
ensemble, and conversion of a collective spin excitation into light. The
proposed scheme should be realizable with current technology, with potential
applications to atomic clocks and magnetometry.Comment: 3 pages, 1 figur
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