110 research outputs found
Impedance-matched cavity quantum memory
We consider an atomic frequency comb based quantum memory inside an
asymmetric optical cavity. In this configuration it is possible to absorb the
input light completely in a system with an effective optical depth of one,
provided that the absorption per cavity round trip exactly matches the
transmission of the coupling mirror ("impedance matching"). We show that the
impedance matching results in a readout efficiency only limited by irreversible
atomic dephasing, whose effect can be made very small in systems with large
inhomogeneous broadening. Our proposal opens up an attractive route towards
quantum memories with close to unit efficiency.Comment: 4 pages, 2 figure
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
Spectral noise in quantum frequency down-conversion from the visible to the telecommunication C-band
We report a detailed study of the noise properties of a visible-to-telecom
photon frequency converter based on difference frequency generation (DFG). The
device converts 580 nm photons to 1541 nm using a strong pump laser at 930 nm,
in a periodically poled lithium niobate ridge waveguide. The converter reaches
a maximum device efficiency of 46 % (internal efficiency of 67 %) at a pump
power of 250 mW. The noise produced by the pump laser is investigated in detail
by recording the noise spectra both in the telecom and visible regimes, and
measuring the power dependence of the noise rates. The noise spectrum in the
telecom is very broadband, as expected from previous work on similar DFG
converters. However, we also observe several narrow dips in the telecom
spectrum, with corresponding peaks appearing in the 580 nm noise spectrum.
These features are explained by sum frequency generation of the telecom noise
at wavelengths given by the phase matching condition of different spatial modes
in the waveguide. The proposed noise model is in good agreement with all the
measured data, including the power-dependence of the noise rates, both in the
visible and telecom regime. These results are applicable to the class of DFG
converters where the pump laser wavelength is in between the input and target
wavelength.Comment: 10 page
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
Multi-mode and long-lived quantum correlations between photons and spins in a crystal
The realization of quantum networks and quantum repeaters remains an
outstanding challenge in quantum communication. These rely on entanglement of
remote matter systems, which in turn requires creation of quantum correlations
between a single photon and a matter system. A practical way to establish such
correlations is via spontaneous Raman scattering in atomic ensembles, known as
the DLCZ scheme. However, time multiplexing is inherently difficult using this
method, which leads to low communication rates even in theory. Moreover, it is
desirable to find solid-state ensembles where such matter-photon correlations
could be generated. Here we demonstrate quantum correlations between a single
photon and a spin excitation in up to 12 temporal modes, in a Eu
doped YSiO crystal, using a novel DLCZ approach that is inherently
multimode. After a storage time of 1 ms, the spin excitation is converted into
a second photon. The quantum correlation of the generated photon pair is
verified by violating a Cauchy - Schwarz inequality. Our results show that
solid-state rare-earth crystals could be used to generate remote multi-mode
entanglement, an important resource for future quantum networks
Analysis of a quantum memory for photons based on controlled reversible inhomogeneous broadening
We present a detailed analysis of a quantum memory for photons based on
controlled and reversible inhomogeneous broadening (CRIB). The explicit
solution of the equations of motion is obtained in the weak excitation regime,
making it possible to gain insight into the dependence of the memory efficiency
on the optical depth, and on the width and shape of the atomic spectral
distributions. We also study a simplified memory protocol which does not
require any optical control fields.Comment: 9 pages, 4 figures (Accepted for publication in Phys. Rev. A
High precision measurement of the Dzyaloshinsky-Moriya interaction between two rare-earth ions in a solid
We report on a direct measurement of the pair-wise anti-symmetric exchange
interaction, known as the Dzyaloshinsky-Moriya interaction (DMI), in a
Nd3+-doped YVO4 crystal. To this end we introduce a broadband electron spin
resonance technique coupled with an optical detection scheme which selectively
detects only one Nd3+-Nd3+ pair. Using this technique we can fully determine
the spin-spin coupling tensor, allowing us to experimentally determine both the
strength and direction of the DMI vector. We believe that this ability to fully
determine the interaction Hamiltonian is of interest for studying the numerous
magnetic phenomena where the DMI interaction is of fundamental importance,
including multiferroics. We also detect a singlet-triplet transition within the
pair, with a highly suppressed magnetic-field dependence, which suggests that
such systems could form singlet-triplet qubits with long coherence times for
quantum information applications
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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