32 research outputs found
Efficient optical pumping using hyperfine levels in Nd:YSiO and its application to optical storage
Efficient optical pumping is an important tool for state initialization in
quantum technologies, such as optical quantum memories. In crystals doped with
Kramers rare-earth ions, such as erbium and neodymium, efficient optical
pumping is challenging due to the relatively short population lifetimes of the
electronic Zeeman levels, of the order of 100 ms at around 4 K. In this article
we show that optical pumping of the hyperfine levels in isotopically enriched
Nd:YSiO crystals is more efficient, owing to the longer
population relaxation times of hyperfine levels. By optically cycling the
population many times through the excited state a nuclear-spin flip can be
forced in the ground-state hyperfine manifold, in which case the population is
trapped for several seconds before relaxing back to the pumped hyperfine level.
To demonstrate the effectiveness of this approach in applications we perform an
atomic frequency comb memory experiment with 33% storage efficiency in
Nd:YSiO, which is on a par with results obtained in
non-Kramers ions, e.g. europium and praseodymium, where optical pumping is
generally efficient due to the quenched electronic spin. Efficient optical
pumping in neodymium-doped crystals is also of interest for spectral filtering
in biomedical imaging, as neodymium has an absorption wavelength compatible
with tissue imaging. In addition to these applications, our study is of
interest for understanding spin dynamics in Kramers ions with nuclear spin.Comment: 8 pages, 6 figure
Quantifying photonic high-dimensional entanglement
High-dimensional entanglement offers promising perspectives in quantum
information science. In practice, however, the main challenge is to devise
efficient methods to characterize high-dimensional entanglement, based on the
available experimental data which is usually rather limited. Here we report the
characterization and certification of high-dimensional entanglement in photon
pairs, encoded in temporal modes. Building upon recently developed theoretical
methods, we certify an entanglement of formation of 2.09(7) ebits in a time-bin
implementation, and 4.1(1) ebits in an energy-time implementation. These
results are based on very limited sets of local measurements, which illustrates
the practical relevance of these methods.Comment: 5 pages, 3 figure
A source of polarization-entangled photon pairs interfacing quantum memories with telecom photons
We present a source of polarization-entangled photon pairs suitable for the
implementation of long-distance quantum communication protocols using quantum
memories. Photon pairs with wavelengths 883 nm and 1338 nm are produced by
coherently pumping two periodically poled nonlinear waveguides embedded in the
arms of a polarization interferometer. Subsequent spectral filtering reduces
the bandwidth of the photons to 240 MHz. The bandwidth is well-matched to a
quantum memory based on an Nd:YSO crystal, to which, in addition, the center
frequency of the 883 nm photons is actively stabilized. A theoretical model
that includes the effect of the filtering is presented and accurately fits the
measured correlation functions of the generated photons. The model can also be
used as a way to properly assess the properties of the source. The quality of
the entanglement is revealed by a visibility of V = 96.1(9)% in a Bell-type
experiment and through the violation of a Bell inequality.Comment: 15 pages, 8 figures, 3 table
Characterization of the hyperfine interaction of the excited D state of Eu:YSiO
We characterize the Europium (Eu) hyperfine interaction of the excited
state (D) and determine its effective spin Hamiltonian parameters for
the Zeeman and quadrupole tensors. An optical free induction decay method is
used to measure all hyperfine splittings under weak external magnetic field (up
to 10 mT) for various field orientations. On the basis of the determined
Hamiltonian we discuss the possibility to predict optical transition
probabilities between hyperfine levels for the FD transition. The obtained results provide necessary information to
realize an optical quantum memory scheme which utilizes long spin coherence
properties of Eu:YSiO material under external magnetic
field
Experimental certification of millions of genuinely entangled atoms in a solid
Quantum theory predicts that entanglement can also persist in macroscopic
physical systems, albeit difficulties to demonstrate it experimentally remain.
Recently, significant progress has been achieved and genuine entanglement
between up to 2900 atoms was reported. Here we demonstrate 16 million genuinely
entangled atoms in a solid-state quantum memory prepared by the heralded
absorption of a single photon. We develop an entanglement witness for
quantifying the number of genuinely entangled particles based on the collective
effect of directed emission combined with the nonclassical nature of the
emitted light. The method is applicable to a wide range of physical systems and
is effective even in situations with significant losses. Our results clarify
the role of multipartite entanglement in ensemble-based quantum memories as a
necessary prerequisite to achieve a high single-photon process fidelity crucial
for future quantum networks. On a more fundamental level, our results reveal
the robustness of certain classes of multipartite entangled states, contrary
to, e.g., Schr\"odinger-cat states, and that the depth of entanglement can be
experimentally certified at unprecedented scales.Comment: 11 pages incl. Methods and Suppl. Info., 4 figures, 1 table. v2:
close to published version. See also parallel submission by Zarkeshian et al
(1703.04709
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
Quantum teleportation from a telecom-wavelength photon to a solid-state quantum memory
In quantum teleportation, the state of a single quantum system is disembodied
into classical information and purely quantum correlations, to be later
reconstructed onto a second system that has never directly interacted with the
first one. This counterintuitive phenomenon is a cornerstone of quantum
information science due to its essential role in several important tasks such
as the long-distance transmission of quantum information using quantum
repeaters. In this context, a challenge of paramount importance is the
distribution of entanglement between remote nodes, and to use this entanglement
as a resource for long-distance light-to-matter quantum teleportation. Here we
demonstrate quantum teleportation of the polarization state of a
telecom-wavelength photon onto the state of a solid-state quantum memory.
Entanglement is established between a rare-earth-ion doped crystal storing a
single photon that is polarization-entangled with a flying telecom-wavelength
photon. The latter is jointly measured with another flying qubit carrying the
polarization state to be teleported, which heralds the teleportation. The
fidelity of the polarization state of the photon retrieved from the memory is
shown to be greater than the maximum fidelity achievable without entanglement,
even when the combined distances travelled by the two flying qubits is 25 km of
standard optical fibre. This light-to-matter teleportation channel paves the
way towards long-distance implementations of quantum networks with solid-state
quantum memories.Comment: 5 pages (main text) + appendix (10 pages
High-fidelity multi-photon-entangled cluster state with solid-state quantum emitters in photonic nanostructures
We propose a complete architecture for deterministic generation of entangled
multiphoton states. Our approach utilizes periodic driving of a quantum-dot
emitter and an efficient light-matter interface enabled by a photonic crystal
waveguide. We assess the quality of the photonic states produced from a real
system by including all intrinsic experimental imperfections. Importantly, the
protocol is robust against the nuclear spin bath dynamics due to a naturally
built-in refocussing method reminiscent to spin echo. We demonstrate the
feasibility of producing Greenberger-Horne-Zeilinger and one-dimensional
cluster states with fidelities and generation rates exceeding those achieved
with conventional 'fusion' methods in current state-of-the-art experiments. The
proposed hardware constitutes a scalable and resource-efficient approach
towards implementation of measurement-based quantum communication and
computing
Temporal multimode storage of entangled photon pairs
Multiplexed quantum memories capable of storing and processing entangled
photons are essential for the development of quantum networks. In this context,
we demonstrate the simultaneous storage and retrieval of two entangled photons
inside a solid-state quantum memory and measure a temporal multimode capacity
of ten modes. This is achieved by producing two polarization entangled pairs
from parametric down conversion and mapping one photon of each pair onto a
rare-earth-ion doped (REID) crystal using the atomic frequency comb (AFC)
protocol. We develop a concept of indirect entanglement witnesses, which can be
used as Schmidt number witness, and we use it to experimentally certify the
presence of more than one entangled pair retrieved from the quantum memory. Our
work puts forward REID-AFC as a platform compatible with temporal multiplexing
of several entangled photon pairs along with a new entanglement certification
method useful for the characterisation of multiplexed quantum memories
A coherent spin-photon interface with waveguide induced cycling transitions
Solid-state quantum dots are promising candidates for efficient light-matter
interfaces connecting internal spin degrees of freedom to the states of emitted
photons. However, selection rules prevent the combination of efficient spin
control and optical cyclicity in this platform. By utilizing a photonic crystal
waveguide we here experimentally demonstrate optical cyclicity up to
through photonic state engineering while achieving high fidelity
spin initialization and coherent optical spin control. These capabilities pave
the way towards scalable multi-photon entanglement generation and on-chip
spin-photon gates.Comment: 5 pages, 4 figure