14 research outputs found
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
Robust entanglement generation by reservoir engineering
Following a recent proposal [C. Muschik et. al., Phys. Rev. A 83, 052312
(2011)], engineered dissipative processes have been used for the generation of
stable entanglement between two macroscopic atomic ensembles at room
temperature [H. Krauter et. al., Phys. Rev. Lett. 107, 080503 (2011)]. This
experiment included the preparation of entangled states which are continuously
available during a time interval of one hour. Here, we present additional
material, further-reaching data and an extension of the theory developed in [C.
Muschik et. al., Phys. Rev. A 83, 052312 (2011)]. In particular, we show how
the combination of the entangling dissipative mechanism with measurements can
give rise to a substantial improvement of the generated entanglement in the
presence of noise.Comment: Submitted to Journal of Physics B, special issue on "Quantum Memory
Entanglement generated by dissipation and steady state entanglement of two macroscopic objects
Entanglement is a striking feature of quantum mechanics and an essential
ingredient in most applications in quantum information. Typically, coupling of
a system to an environment inhibits entanglement, particularly in macroscopic
systems. Here we report on an experiment, where dissipation continuously
generates entanglement between two macroscopic objects. This is achieved by
engineering the dissipation using laser- and magnetic fields, and leads to
robust event-ready entanglement maintained for 0.04s at room temperature. Our
system consists of two ensembles containing about 10^{12} atoms and separated
by 0.5m coupled to the environment composed of the vacuum modes of the
electromagnetic field. By combining the dissipative mechanism with a continuous
measurement, steady state entanglement is continuously generated and observed
for up to an hour.Comment: This is an update of the preprint from June 2010. It includes new
results on the creation of steady state entanglement, which has been
maintained up to one hou
Quantum teleportation between light and matter
Quantum teleportation is an important ingredient in distributed quantum
networks, and can also serve as an elementary operation in quantum computers.
Teleportation was first demonstrated as a transfer of a quantum state of light
onto another light beam; later developments used optical relays and
demonstrated entanglement swapping for continuous variables. The teleportation
of a quantum state between two single material particles (trapped ions) has now
also been achieved. Here we demonstrate teleportation between objects of a
different nature - light and matter, which respectively represent 'flying' and
'stationary' media. A quantum state encoded in a light pulse is teleported onto
a macroscopic object (an atomic ensemble containing 10^12 caesium atoms).
Deterministic teleportation is achieved for sets of coherent states with mean
photon number (n) up to a few hundred. The fidelities are 0.58+-0.02 for n=20
and 0.60+-0.02 for n=5 - higher than any classical state transfer can possibly
achieve. Besides being of fundamental interest, teleportation using a
macroscopic atomic ensemble is relevant for the practical implementation of a
quantum repeater. An important factor for the implementation of quantum
networks is the teleportation distance between transmitter and receiver; this
is 0.5 metres in the present experiment. As our experiment uses propagating
light to achieve the entanglement of light and atoms required for
teleportation, the present approach should be scalable to longer distances.Comment: 23 pages, 8 figures, incl. supplementary informatio
Community psychology and counselling psychology: developing collaborative ways of working
We analyse a novel squeezing and entangling mechanism which is due to
correlated Stokes and anti-Stokes photon forward scattering in a multi-level
atom vapour. Following the proposal we present an experimental demonstration of
3.5 dB pulsed frequency nondegenerate squeezed (quadrature entangled) state of
light using room temperature caesium vapour. The source is very robust and
requires only a few milliwatts of laser power. The squeezed state is generated
in the same spatial mode as the local oscillator and in a single temporal mode.
The two entangled modes are separated by twice the Zeeman frequency of the
vapour which can be widely tuned. The narrow-band squeezed light generated near
an atomic resonance can be directly used for atom-based quantum information
protocols. Its single temporal mode characteristics make it a promising
resource for quantum information processing