2 research outputs found
Experimental demonstration of quantum memory for light
The information carrier of today's communications, a weak pulse of light, is
an intrinsically quantum object. As a consequence, complete information about
the pulse cannot, even in principle, be perfectly recorded in a classical
memory. In the field of quantum information this has led to a long standing
challenge: how to achieve a high-fidelity transfer of an independently prepared
quantum state of light onto the atomic quantum state? Here we propose and
experimentally demonstrate a protocol for such quantum memory based on atomic
ensembles. We demonstrate for the first time a recording of an externally
provided quantum state of light onto the atomic quantum memory with a fidelity
up to 70%, significantly higher than that for the classical recording. Quantum
storage of light is achieved in three steps: an interaction of light with
atoms, the subsequent measurement on the transmitted light, and the feedback
onto the atoms conditioned on the measurement result. Density of recorded
states 33% higher than that for the best classical recording of light on atoms
is achieved. A quantum memory lifetime of up to 4 msec is demonstrated.Comment: 22 pages (double line spacing) incl. supplementary information, 4
figures, accepted for publication in Natur
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