10 research outputs found
Manipulating time-bin qubits with fiber optics components
We propose two experimental schemes to implement arbitrary unitary single
qubit operations on single photons encoded in time-bin qubits. Both schemes
require fiber optics components that are available with current technology.Comment: 2 pages, 3 figures, to be published in the proceedings of the IEEE
LEOS 2006 topical meeting, Quebec city, Canada, July 200
Exploring Macroscopic Entanglement with a Single Photon and Coherent States
Entanglement between macroscopically populated states can easily be created
by combining a single photon and a bright coherent state on a beam-splitter.
Motivated by the simplicity of this technique, we report on a method using
displacement operations in the phase space and basic photon detections to
reveal such an entanglement. We demonstrate through preliminary experimental
results, that this eminently feasible approach provides an attractive way for
exploring entanglement at various scales, ranging from one to a thousand
photons. This offers an instructive viewpoint to gain insight into the reasons
that make it hard to observe quantum features in our macroscopic world.Comment: 6 pages, 10 figures. v2: Updated version. The corresponding
experiment is reported in arXiv:1212.3710. See also arXiv:1306.084
Detector-Device-Independent Quantum Key Distribution
Recently, a quantum key distribution (QKD) scheme based on entanglement
swapping, called measurement-device-independent QKD (mdiQKD), was proposed to
bypass all detector side-channel attacks. While mdiQKD is conceptually elegant
and offers a supreme level of security, the experimental complexity is
challenging for practical systems. For instance, it requires interference
between two widely separated independent single-photon sources, and the rates
are dependent on detecting two photons - one from each source. Here we
experimentally demonstrate a QKD scheme that removes the need for a two-photon
system and instead uses the idea of a two-qubit single-photon (TQSP) to
significantly simplify the implementation and improve the efficiency of mdiQKD
in several aspects.Comment: 5 pages + 3 figure
Fast and simple characterization of a photon pair source
We present an exact model of the detection statistics of a probabilistic
source of photon pairs from which a fast, simple and precise method to measure
the source's brightness and photon channel transmissions is demonstrated. We
measure such properties for a source based on spontaneous parametric
downconversion in a periodically poled LiNbO crystal producing pairs at 810
and 1550 nm wavelengths. We further validate the model by comparing the
predicted and measured values for the of a heralded single photon
source over a wide range of the brightness. Our model is of particular use for
monitoring and tuning the brightness on demand as required for various quantum
communication applications. We comment on its applicability to sources
involving spectral and/or spatial filtering.Comment: 10 pages, 5 figures. Published versio
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
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
Storage of hyperentanglement in a solid-state quantum memory
Two photons can simultaneously share entanglement between several degrees of
freedom such as polarization, energy-time, spatial mode and orbital angular
momentum. This resource is known as hyperentanglement, and it has been shown to
be an important tool for optical quantum information processing. Here we
demonstrate the quantum storage and retrieval of photonic hyperentanglement in
a solid-state quantum memory. A pair of photons entangled in polarization and
energy-time is generated such that one photon is stored in the quantum memory,
while the other photon has a telecommunication wavelength suitable for
transmission in optical fibre. We measured violations of a
Clauser-Horne-Shimony-Holt (CHSH) Bell inequality for each degree of freedom,
independently of the other one, which proves the successful storage and
retrieval of the two bits of entanglement shared by the photons. Our scheme is
compatible with long-distance quantum communication in optical fibre, and is in
particular suitable for linear-optical entanglement purification for quantum
repeaters