45 research outputs found
A solid state spin-wave quantum memory for time-bin qubits
We demonstrate the first solid-state spin-wave optical quantum memory with
on-demand read-out. Using the full atomic frequency comb scheme in a \PrYSO
crystal, we store weak coherent pulses at the single-photon level with a signal
to noise ratio . Narrow-band spectral filtering based on spectral hole
burning in a second \PrYSO crystal is used to filter out the excess noise
created by control pulses to reach an unconditional noise level of photons per pulse. We also report spin-wave storage of
photonic time-bin qubits with conditional fidelities higher than a measure and
prepare strategy, demonstrating that the spin-wave memory operates in the
quantum regime. This makes our device the first demonstration of a quantum
memory for time-bin qubits, with on demand read-out of the stored quantum
information. These results represent an important step for the use of
solid-state quantum memories in scalable quantum networks.Comment: 10 pages, 10 figure
Photon echo without a free induction decay in a double-Lambda system
We have characterized a novel photon-echo pulse sequence for a
double- type energy level system where the input and rephasing
transitions are different to the applied -pulses. We show that despite
having imperfect -pulses (associated with large coherent emission due to
free induction decay), the noise added is only 0.0190.001 relative to the
shot noise in the spectral mode of the echo. Using this echo pulse sequence in
the `rephased amplified spontaneous emission' (RASE) scheme
\cite{Ledingham2010} will allow for generation of entangled photon pairs that
are in different frequency, temporal, and potentially spatial modes to any
bright driving fields. The coherence and efficiency properties of this sequence
were characterized in a Pr:YSO crystal
Coherent Storage of Temporally Multimode Light Using a Spin-Wave Atomic Frequency Comb Memory
We report on coherent and multi-temporal mode storage of light using the full
atomic frequency comb memory scheme. The scheme involves the transfer of
optical atomic excitations in Pr3+:Y2SiO5 to spin-waves in the hyperfine levels
using strong single-frequency transfer pulses. Using this scheme, a total of 5
temporal modes are stored and recalled on-demand from the memory. The coherence
of the storage and retrieval is characterized using a time-bin interference
measurement resulting in visibilities higher than 80%, independent of the
storage time. This coherent and multimode spin-wave memory is promising as a
quantum memory for light.Comment: 17 pages, 5 figure
Non-classical photon streams using rephased amplified spontaneous emission
We present a fully quantum mechanical treatment of optically rephased photon
echoes. These echoes exhibit noise due to amplified spontaneous emission,
however this noise can be seen as a consequence of the entanglement between the
atoms and the output light. With a rephasing pulse one can get an "echo" of the
amplified spontaneous emission, leading to light with nonclassical correlations
at points separated in time, which is of interest in the context of building
wide bandwidth quantum repeaters. We also suggest a wideband version of DLCZ
protocol based on the same ideas.Comment: 5 pages, 4 figures. Added section
Storage of up-converted telecom photons in a doped crystal
We report on an experiment that demonstrates the frequency up-conversion of
telecommunication wavelength single-photon-level pulses to be resonant with a
: crystal. We convert
the telecom photons at to using a
periodically-poled potassium titanyl phosphate nonlinear waveguide. The maximum
device efficiency (which includes all optical loss) is inferred to be
(internal efficiency
) with a signal to noise ratio exceeding 1 for
single-photon-level pulses with durations of up to 560ns. The converted
light is then stored in the crystal using the atomic frequency comb scheme with
storage and retrieval efficiencies exceeding for
predetermined storage times of up to . The retrieved light is
time delayed from the noisy conversion process allowing us to measure a signal
to noise ratio exceeding 100 with telecom single-photon-level inputs. These
results represent the first demonstration of single-photon-level optical
storage interfaced with frequency up-conversion
Experimental realization of light with time separated correlations by rephasing amplified spontaneous emission
Amplified spontaneous emission is a common noise source in active optical
systems, it is generally seen as being an incoherent process. Here we excite an
ensemble of rare earth ion dopants in a solid with a {\pi}-pulse, resulting in
amplified spontaneous emission. The application of a second {\pi}-pulse leads
to a coherent echo of the amplified spontaneous emission that is correlated in
both amplitude and phase. For small optical thicknesses, we see evidence that
the amplified spontaneous emission and its echo are entangled.Comment: 6 pages, 5 figures, the supplementary information pdf was uploaded
with latex source files. This version accepted for publication in PR
Quantum Storage of a Photonic Polarization Qubit in a Solid
We report on the quantum storage and retrieval of photonic polarization
quantum bits onto and out of a solid state storage device. The qubits are
implemented with weak coherent states at the single photon level, and are
stored for 500 ns in a praseodymium doped crystal with a storage and retrieval
efficiency of 10%, using the atomic frequency comb scheme. We characterize the
storage by using quantum state tomography, and find that the average
conditional fidelity of the retrieved qubits exceeds 95% for a mean photon
number mu=0.4. This is significantly higher than a classical benchmark, taking
into account the Poissonian statistics and finite memory efficiency, which
proves that our device functions as a quantum storage device for polarization
qubits, even if tested with weak coherent states. These results extend the
storage capabilities of solid state quantum memories to polarization encoding,
which is widely used in quantum information science.Comment: 6 pages, 6 figures, 1 table. New reference adde
Raman Quantum Memory with Built-In Suppression of Four-wave Mixing Noise
Quantum memories are essential for large-scale quantum information networks.
Along with high efficiency, storage lifetime and optical bandwidth, it is
critical that the memory add negligible noise to the recalled signal. A common
source of noise in optical quantum memories is spontaneous four-wave mixing. We
develop and implement a technically simple scheme to suppress this noise
mechanism by means of quantum interference. Using this scheme with a Raman
memory in warm atomic vapour we demonstrate over an order of magnitude
improvement in noise performance. Furthermore we demonstrate a method to
quantify the remaining noise contributions and present a route to enable
further noise suppression. Our scheme opens the way to quantum demonstrations
using a broadband memory, significantly advancing the search for scalable
quantum photonic networks.Comment: 6 pages, 5 figures plus Supplementary Materia
Experimental demonstration of quantum effects in the operation of microscopic heat engines
The heat engine, a machine that extracts useful work from thermal sources, is
one of the basic theoretical constructs and fundamental applications of
classical thermodynamics. The classical description of a heat engine does not
include coherence in its microscopic degrees of freedom. By contrast, a quantum
heat engine might possess coherence between its internal states. Although the
Carnot efficiency cannot be surpassed, and coherence can be performance
degrading in certain conditions, it was recently predicted that even when using
only thermal resources, internal coherence can enable a quantum heat engine to
produce more power than any classical heat engine using the same resources.
Such a power boost therefore constitutes a quantum thermodynamic signature. It
has also been shown that the presence of coherence results in the thermodynamic
equivalence of different quantum heat engine types, an effect with no classical
counterpart. Microscopic heat machines have been recently implemented with
trapped ions, and proposals for heat machines using superconducting circuits
and optomechanics have been made. When operated with standard thermal baths,
however, the machines implemented so far have not demonstrated any inherently
quantum feature in their thermodynamic quantities. Here we implement two types
of quantum heat engines by use of an ensemble of nitrogen-vacancy centres in
diamond, and experimentally demonstrate both the coherence power boost and the
equivalence of different heat-engine types. This constitutes the first
observation of quantum thermodynamic signatures in heat machines