15,432 research outputs found
Photonic quantum state transfer between a cold atomic gas and a crystal
Interfacing fundamentally different quantum systems is key to build future
hybrid quantum networks. Such heterogeneous networks offer superior
capabilities compared to their homogeneous counterparts as they merge
individual advantages of disparate quantum nodes in a single network
architecture. However, only very few investigations on optical
hybrid-interconnections have been carried out due to the high fundamental and
technological challenges, which involve e.g. wavelength and bandwidth matching
of the interfacing photons. Here we report the first optical quantum
interconnection between two disparate matter quantum systems with photon
storage capabilities. We show that a quantum state can be faithfully
transferred between a cold atomic ensemble and a rare-earth doped crystal via a
single photon at telecommunication wavelength, using cascaded quantum frequency
conversion. We first demonstrate that quantum correlations between a photon and
a single collective spin excitation in the cold atomic ensemble can be
transferred onto the solid-state system. We also show that single-photon
time-bin qubits generated in the cold atomic ensemble can be converted, stored
and retrieved from the crystal with a conditional qubit fidelity of more than
. Our results open prospects to optically connect quantum nodes with
different capabilities and represent an important step towards the realization
of large-scale hybrid quantum networks
On-demand semiconductor single-photon source with near-unity indistinguishability
Single photon sources based on semiconductor quantum dots offer distinct
advantages for quantum information, including a scalable solid-state platform,
ultrabrightness, and interconnectivity with matter qubits. A key prerequisite
for their use in optical quantum computing and solid-state networks is a high
level of efficiency and indistinguishability. Pulsed resonance fluorescence
(RF) has been anticipated as the optimum condition for the deterministic
generation of high-quality photons with vanishing effects of dephasing. Here,
we generate pulsed RF single photons on demand from a single,
microcavity-embedded quantum dot under s-shell excitation with 3-ps laser
pulses. The pi-pulse excited RF photons have less than 0.3% background
contributions and a vanishing two-photon emission probability.
Non-postselective Hong-Ou-Mandel interference between two successively emitted
photons is observed with a visibility of 0.97(2), comparable to trapped atoms
and ions. Two single photons are further used to implement a high-fidelity
quantum controlled-NOT gate.Comment: 11 pages, 11 figure
Visual assessment of multi-photon interference
Classical machine learning algorithms can provide insights on high-dimensional processes that are hardly accessible with conventional approaches. As a notable example, t-distributed Stochastic Neighbor Embedding (t-SNE) represents the state of the art for visualization of data sets of large dimensionality. An interesting question is then if this algorithm can provide useful information also in quantum experiments with very large Hilbert spaces. Leveraging these considerations, in this work we apply t-SNE to probe the spatial distribution of n-photon events in m-dimensional Hilbert spaces, showing that its findings can be beneficial for validating genuine quantum interference in boson sampling experiments. In particular, we find that nonlinear dimensionality reduction is capable to capture distinctive features in the spatial distribution of data related to multi-photon states with different evolutions. We envisage that this approach will inspire further theoretical investigations, for instance for a reliable assessment of quantum computational advantage
Conditional control of the quantum states of remote atomic memories for quantum networking
Quantum networks hold the promise for revolutionary advances in information
processing with quantum resources distributed over remote locations via
quantum-repeater architectures. Quantum networks are composed of nodes for
storing and processing quantum states, and of channels for transmitting states
between them. The scalability of such networks relies critically on the ability
to perform conditional operations on states stored in separated quantum
memories. Here we report the first implementation of such conditional control
of two atomic memories, located in distinct apparatuses, which results in a
28-fold increase of the probability of simultaneously obtaining a pair of
single photons, relative to the case without conditional control. As a first
application, we demonstrate a high degree of indistinguishability for remotely
generated single photons by the observation of destructive interference of
their wavepackets. Our results demonstrate experimentally a basic principle for
enabling scalable quantum networks, with applications as well to linear optics
quantum computation.Comment: 10 pages, 8 figures; Minor corrections. References updated. Published
at Nature Physics 2, Advanced Online Publication of 10/29 (2006
Purification of Single-photon Entanglement
Single-photon entanglement is a simple form of entanglement that exists
between two spatial modes sharing a single photon. Despite its elementary form,
it provides a resource as useful as polarization-entangled photons and it can
be used for quantum teleportation and entanglement swapping operations. Here,
we report the first experiment where single-photon entanglement is purified
with a simple linear-optics based protocol. Besides its conceptual interest,
this result might find applications in long distance quantum communication
based on quantum repeaters.Comment: Main article: 5 pages, 4 figure
Simulation of Quantum Computation: A deterministic event-based approach
We demonstrate that locally connected networks of machines that have
primitive learning capabilities can be used to perform a deterministic,
event-based simulation of quantum computation. We present simulation results
for basic quantum operations such as the Hadamard and the controlled-NOT gate,
and for seven-qubit quantum networks that implement Shor's numbering factoring
algorithm.Comment: J. Comp. Theor. Nanoscience (in press); http://www.compphys.net/dl
Simple atomic quantum memory suitable for semiconductor quantum dot single photons
Quantum memories matched to single photon sources will form an important
cornerstone of future quantum network technology. We demonstrate such a memory
in warm Rb vapor with on-demand storage and retrieval, based on
electromagnetically induced transparency. With an acceptance bandwidth of
= 0.66~GHz the memory is suitable for single photons emitted by
semiconductor quantum dots. In this regime, vapor cell memories offer an
excellent compromise between storage efficiency, storage time, noise level, and
experimental complexity, and atomic collisions have negligible influence on the
optical coherences. Operation of the memory is demonstrated using attenuated
laser pulses on the single photon level. For 50 ns storage time we measure
\emph{end-to-end efficiency}
of the fiber-coupled memory, with an \emph{total intrinsic efficiency}
. Straightforward technological improvements can
boost the end-to-end-efficiency to ; beyond
that increasing the optical depth and exploiting the Zeeman substructure of the
atoms will allow such a memory to approach near unity efficiency.
In the present memory, the unconditional readout noise level of photons is dominated by atomic fluorescence, and for input pulses
containing on average photons the signal to noise level would
be unity
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