10 research outputs found
An efficient quantum memory based on two-level atoms
We propose a method to implement a quantum memory for light based on
ensembles of two-level atoms. Our protocol is based on controlled reversible
inhomogeneous broadening (CRIB), where an external field first dephases the
atomic polarization and thereby stores an incoming light pulse into collective
states of the atomic ensemble, and later a reversal of the applied field leads
to a rephasing of the atomic polarization and a reemission of the light. As
opposed to previous proposals for CRIB based quantum memories we propose to
only apply the broadening for a short period after most of the pulse has
already been absorbed by the ensemble. We show that with this procedure there
exist certain modes of the incoming light field which can be stored with an
efficiency approaching 100% in the limit of high optical depth and long
coherence time of the atoms. These results demonstrate that it is possible to
operate an efficient quantum memory without any optical control fields
Dispersion relations for stationary light in one-dimensional atomic ensembles
We investigate the dispersion relations for light coupled to one-dimensional
ensembles of atoms with different level schemes. The unifying feature of all
the considered setups is that the forward and backward propagating quantum
fields are coupled by the applied classical drives such that the group velocity
can vanish in an effect known as "stationary light". We derive the dispersion
relations for all the considered schemes, highlighting the important
differences between them. Furthermore, we show that additional control of
stationary light can be obtained by treating atoms as discrete scatterers and
placing them at well defined positions. For the latter purpose, a multi-mode
transfer matrix theory for light is developed
Sequential nonabsorbing microwave single-photon detector
We propose a nonabsorbing microwave single-photon detector that uses an
artificial atom as a coherent interaction mediator between a traveling photon
and a high-Q resonator, fully exploiting the knowledge of the photon's arrival
time. Our proposal can be implemented with the current level of technology and
achieves distinguishability (probability of distinguishing between zero and one
photon) in excess of 98% for realistic parameters. This is better than any of
the similar detector proposals, even the ones using several artificial atoms.Comment: 6 pages, 3 figure
Photonic Controlled-Phase Gates Through Rydberg Blockade in Optical Cavities
We propose a novel scheme for high fidelity photonic controlled phase gates
using Rydberg blockade in an ensemble of atoms in an optical cavity. The gate
operation is obtained by first storing a photonic pulse in the ensemble and
then scattering a second pulse from the cavity, resulting in a phase change
depending on whether the first pulse contained a single photon. We show that
the combination of Rydberg blockade and optical cavities effectively enhances
the optical non-linearity created by the strong Rydberg interaction and thereby
reduces the requirements for photonic quantum gates. The resulting gate can be
implemented with cavities of moderate finesse which allows for highly efficient
processing of quantum information encoded in photons. As a particular example
of this, we show how the gate can be employed to increase the communication
rate of quantum repeaters based on atomic ensembles.Comment: main manuscript 5 pages with 11 pages of supplementary informatio
Controlled-phase Gate for Photons Based on Stationary Light
We propose a method to induce strong effective interactions between photons
mediated by an atomic ensemble. To achieve this, we use the so-called
stationary light effect to enhance the interaction. Regardless of the
single-atom coupling to light, the interaction strength between the photons can
be enhanced by increasing the total number of atoms. For sufficiently many
atoms, the setup can be viable as a controlled-phase gate for photons. We
derive analytical expressions for the fidelities for two modes of gate
operation: deterministic and heralded conditioned on the presence of two
photons at the output.Comment: 5 pages, 3 figures + Supplemental Materia