113 research outputs found
Temporally multiplexed quantum repeaters with atomic gases
We propose a temporally multiplexed version of the Duan-Lukin-Cirac-Zoller
(DLCZ) quantum repeater protocol using controlled inhomogeneous spin broadening
in atomic gases. A first analysis suggests that the advantage of multiplexing
is negated by noise due to spin wave excitations corresponding to unobserved
directions of Stokes photon emission. However, this problem can be overcome
with the help of a moderate-finesse cavity which is in resonance with Stokes
photons, but invisible to the anti-Stokes photons. Our proposal promises
greatly enhanced quantum repeater performance with atomic gases.Comment: 5 pages, 1 figur
Optimal Photon Generation from Spontaneous Raman Processes in Cold Atoms
Spontaneous Raman processes in cold atoms have been widely used in the past
decade for generating single photons. Here, we present a method to optimize
their efficiencies for given atomic coherences and optical depths. We give a
simple and complete recipe that can be used in present-day experiments,
attaining near-optimal single photon emission while preserving the photon
purity.Comment: 6+6 pages, 3 figures, 1 tabl
Creating high dimensional time-bin entanglement using mode-locked lasers
We present a new scheme to generate high dimensional entanglement between two
photonic systems. The idea is based on parametric down conversion with a
sequence of pump pulses generated by a mode-locked laser. We prove
experimentally the feasibility of this scheme by performing a Franson-type Bell
test using a 2-way interferometer with path-length difference equal to the
distance between 2 pump pulses. With this experiment, we can demonstrate
entanglement for a two-photon state of at least dimension D=11. Finally, we
propose a feasible experiment to show a Fabry-Perot like effect for a high
dimensional two-photon state.Comment: 5 pages, 5 figure
Dynamic control of Purcell enhanced emission of erbium ions in nanoparticles
The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons’ waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity.Peer ReviewedPostprint (published version
Mapping multiple photonic qubits into and out of one solid-state atomic ensemble
The future challenge of quantum communication are scalable quantum networks,
which require coherent and reversible mapping of photonic qubits onto
stationary atomic systems (quantum memories). A crucial requirement for
realistic networks is the ability to efficiently store multiple qubits in one
quantum memory. Here we demonstrate coherent and reversible mapping of 64
optical modes at the single photon level in the time domain onto one
solid-state ensemble of rare-earth ions. Our light-matter interface is based on
a high-bandwidth (100 MHz) atomic frequency comb, with a pre-determined storage
time of 1 microseconds. We can then encode many qubits in short <10 ns temporal
modes (time-bin qubits). We show the good coherence of the mapping by
simultaneously storing and analyzing multiple time-bin qubits.Comment: 7 pages, 6 figures + Supplementary materia
Quantum repeaters based on heralded qubit amplifiers
We present a quantum repeater scheme based on the recently proposed qubit
amplifier [N. Gisin, S. Pironio and N. Sangouard, Phys. Rev. Lett. 105, 070501
(2010)]. It relies on a on-demand entangled-photon pair source which uses
on-demand single-photon sources, linear optical elements and atomic ensembles.
Interestingly, the imperfections affecting the states created from this source,
caused e.g. by detectors with non-unit efficiencies, are systematically
purified from an entanglement swapping operation based on a two-photon
detection. This allows the distribution of entanglement over very long
distances with a high fidelity, i.e. without vacuum components and multiphoton
errors. Therefore, the resulting quantum repeater architecture does not
necessitate final postselections and thus achieves high entanglement
distribution rates. This also provides unique opportunities for
device-independent quantum key distribution over long distances with linear
optics and atomic ensembles.Comment: 8 pages, 4 figure
Approaches for a quantum memory at telecommunication wavelengths
We report experimental storage and retrieval of weak coherent states of light
at telecommunication wavelengths using erbium ions doped into a solid. We use
two photon echo based quantum storage protocols. The first one is based on
controlled reversible inhomogeneous broadening (CRIB). It allows the retrieval
of the light on demand by controlling the collective atomic coherence with an
external electric field, via the linear Stark effect. We study how atoms in the
excited state affect the signal to noise ratio of the CRIB memory. Additionally
we show how CRIB can be used to modify the temporal width of the retrieved
light pulse. The second protocol is based on atomic frequency combs (AFC).
Using this protocol we also verify that the reversible mapping is phase
preserving by performing an interference experiment with a local oscillator.
These measurements are enabling steps towards solid state quantum memories at
telecommunication wavelengths. We also give an outlook on possible
improvements.Comment: 13 pages, 11 figure
Spin Wave Storage using Chirped Control Fields in Atomic Frequency Comb based Quantum Memory
It has been shown that an inhomogeneously broadened optical transition shaped
into an atomic frequency comb can store a large number of temporal modes of the
electromagnetic field at the single photon level without the need to increase
the optical depth of the storage material. The readout of light modes is made
efficient thanks to the rephasing of the optical-wavelength coherence similarly
to photon echo-type techniques and the re-emission time is given by the comb
structure. For on-demand readout and long storage times, two control fields are
used to transfer back and forth the optical coherence into a spin wave. Here,
we present a detailed analysis of the spin wave storage based on chirped
adiabatic control fields. In particular, we verify that chirped fields require
significantly weaker intensities than -pulses. The price to pay is a
reduction of the multimode storage capacity that we quantify for realistic
material parameters associated with solids doped with rare-earth-metal ions.Comment: 7 pages, 3 figure
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