18 research outputs found
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
Cavity-enhanced storage in an optical spin-wave memory
We report on the experimental demonstration of an optical spin-wave memory,
based on the atomic frequency comb (AFC) scheme, where the storage efficiency
is strongly enhanced by an optical cavity. The cavity is of low finesse, but
operated in an impedance matching regime to achieve high absorption in our
intrinsically low-absorbing Eu3+:Y2SiO5 crystal. For storage of optical pulses
as an optical excitation (AFC echoes), we reach efficiencies of 53% and 28% for
2 and 10 microseconds delays, respectively. For a complete AFC spin-wave memory
we reach an efficiency of 12%, including spin-wave dephasing, which is a
12-fold increase with respect to previous results in this material. This result
is an important step towards the goal of making efficient and long-lived
quantum memories based on spin waves, in the context of quantum repeaters and
quantum networks
Spectral hole lifetimes and spin population relaxation dynamics in neodymium-doped yttrium orthosilicate
We present a detailed study of the lifetime of optical spectral holes due to
population storage in Zeeman sublevels of Nd:YSiO. The lifetime
is measured as a function of magnetic field strength and orientation,
temperature and Nd doping concentration. At the lowest temperature of 3
K we find a general trend where the lifetime is short at low field strengths,
then increases to a maximum lifetime at a few hundreds of mT, and then finally
decays rapidly for high field strengths. This behaviour can be modelled with a
relaxation rate dominated by Nd-Nd cross relaxation at low fields
and spin lattice relaxation at high magnetic fields. The maximum lifetime
depends strongly on both the field strength and orientation, due to the
competition between these processes and their different angular dependencies.
The cross relaxation limits the maximum lifetime for concentrations as low as
30 ppm of Nd ions. By decreasing the concentration to less than 1 ppm we
could completely eliminate the cross relaxation, reaching a lifetime of 3.8 s
at 3~K. At higher temperatures the spectral hole lifetime is limited by the
magnetic-field independent Raman and Orbach processes. In addition we show that
the cross relaxation rate can be strongly reduced by creating spectrally large
holes of the order of the optical inhomogeneous broadening. Our results are
important for the development and design of new rare-earth-ion doped crystals
for quantum information processing and narrow-band spectral filtering for
biological tissue imaging
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
Demonstration of atomic frequency comb memory for light with spin-wave storage
We present a light-storage experiment in a praseodymium-doped crystal where
the light is mapped onto an inhomogeneously broadened optical transition shaped
into an atomic frequency comb. After absorption of the light the optical
excitation is converted into a spin-wave excitation by a control pulse. A
second control pulse reads the memory (on-demand) by reconverting the spin-wave
excitation to an optical one, where the comb structure causes a photon-echo
type rephasing of the dipole moments and directional retrieval of the light.
This combination of photon echo and spin-wave storage allows us to store
sub-microsecond (450ns) pulses for up to 20 microseconds. The scheme has a high
potential for storing multiple temporal modes in the single photon regime,
which is an important resource for future long-distance quantum communication
based on quantum repeaters.Comment: Final version. 4 pages, 5 figure
Quantum Storage of Photonic Entanglement in a Crystal
Entanglement is the fundamental characteristic of quantum physics. Large
experimental efforts are devoted to harness entanglement between various
physical systems. In particular, entanglement between light and material
systems is interesting due to their prospective roles as "flying" and
stationary qubits in future quantum information technologies, such as quantum
repeaters and quantum networks. Here we report the first demonstration of
entanglement between a photon at telecommunication wavelength and a single
collective atomic excitation stored in a crystal. One photon from an
energy-time entangled pair is mapped onto a crystal and then released into a
well-defined spatial mode after a predetermined storage time. The other photon
is at telecommunication wavelength and is sent directly through a 50 m fiber
link to an analyzer. Successful transfer of entanglement to the crystal and
back is proven by a violation of the Clauser-Horne-Shimony-Holt (CHSH)
inequality by almost three standard deviations (S=2.64+/-0.23). These results
represent an important step towards quantum communication technologies based on
solid-state devices. In particular, our resources pave the way for building
efficient multiplexed quantum repeaters for long-distance quantum networks.Comment: 5 pages, 3 figures + supplementary information; fixed typo in ref.
[36
Heralded quantum entanglement between two crystals
Quantum networks require the crucial ability to entangle quantum nodes. A
prominent example is the quantum repeater which allows overcoming the distance
barrier of direct transmission of single photons, provided remote quantum
memories can be entangled in a heralded fashion. Here we report the observation
of heralded entanglement between two ensembles of rare-earth-ions doped into
separate crystals. A heralded single photon is sent through a 50/50
beamsplitter, creating a single-photon entangled state delocalized between two
spatial modes. The quantum state of each mode is subsequently mapped onto a
crystal, leading to an entangled state consisting of a single collective
excitation delocalized between two crystals. This entanglement is revealed by
mapping it back to optical modes and by estimating the concurrence of the
retrieved light state. Our results highlight the potential of rare-earth-ions
doped crystals for entangled quantum nodes and bring quantum networks based on
solid-state resources one step closer.Comment: 10 pages, 5 figure
Rare-earth quantum memories for single photons and entanglement
The ability of storing and retrieving quantum states of light is an important experimental challenge in quantum information science. A powerful quantum memory for light is required in a quantum repeater, which would allow long distance (>500km) quantum communications. To be implemented in such application, the quantum memory must allow on-demand readout, with high fidelity and efficiency, and a long storage time. Additionally a multimode capacity (for temporal or spatial modes) would allow multiplexing. Our approaches focus on rare-earth doped crystals, i.e. solid state quantum memory. I present, in this work, our contributions for a solid-state quantum storage, with good performances in every criteria. In particular, I present the preservation of quantum entanglement during the storage, which paves the way for the implementation of quantum memories in quantum repeaters
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