128 research outputs found
A Deterministic and Storable Single-Photon Source Based on Quantum Memory
A single photon source is realized with a cold atomic ensemble (Rb
atoms). In the experiment, single photons, which is initially stored in an
atomic quantum memory generated by Raman scattering of a laser pulse, can be
emitted deterministically at a time-delay in control. It is shown that
production rate of single photons can be enhanced by a feedback circuit
considerably while the single-photon quality is conserved. Thus our present
single-photon source is well suitable for future large-scale realization of
quantum communication and linear optical quantum computation
High speed self-testing quantum random number generation without detection loophole
Quantum mechanics provides means of generating genuine randomness that is
impossible with deterministic classical processes. Remarkably, the
unpredictability of randomness can be certified in a self-testing manner that
is independent of implementation devices. Here, we present an experimental
demonstration of self-testing quantum random number generation based on an
detection-loophole free Bell test with entangled photons. In the randomness
analysis, without the assumption of independent identical distribution, we
consider the worst case scenario that the adversary launches the most powerful
attacks against quantum adversary. After considering statistical fluctuations
and applying an 80 Gb 45.6 Mb Toeplitz matrix hashing, we achieve a
final random bit rate of 114 bits/s, with a failure probability less than
. Such self-testing random number generators mark a critical step
towards realistic applications in cryptography and fundamental physics tests.Comment: 34 pages, 10 figure
Quantum Memory with Optically Trapped Atoms
We report the experimental demonstration of a quantum memory for collective
atomic states in a far-detuned optical dipole trap. Generation of the
collective atomic state is heralded by the detection of a Raman scattered
photon and accompanied by storage in the ensemble of atoms. The optical dipole
trap provides confinement for the atoms during the quantum storage while
retaining the atomic coherence. We probe the quantum storage by
cross-correlation of the photon pair arising from the Raman scattering and the
retrieval of the atomic state stored in the memory. Non-classical correlations
are observed for storage times up to 60 microseconds.Comment: 4 pages, 3 figure
Simultaneous compression of the passively mode-locked pulsewidth and pulse train
Simultaneous compression of the passively mode-locked pulse width and pulse train have been achieved by using a plano-convex unstable resonator hybrided by a nonlinear Sagnac ring interferometer. The greater than 30 mJ single pulse energy of a lone oscillator and less than or equal to 10 ps pulsewidth have been obtained. Using this system, the LAGEOS and ETALON satellites' laser ranging have been performed successfully
Memory-built-in quantum teleportation with photonic and atomic qubits
The combination of quantum teleportation and quantum memory of photonic
qubits is essential for future implementations of large-scale quantum
communication and measurement-based quantum computation. Both steps have been
achieved separately in many proof-of-principle experiments, but the
demonstration of memory-built-in teleportation of photonic qubits remains an
experimental challenge. Here, we demonstrate teleportation between photonic
(flying) and atomic (stationary) qubits. In our experiment, an unknown
polarization state of a single photon is teleported over 7 m onto a remote
atomic qubit that also serves as a quantum memory. The teleported state can be
stored and successfully read out for up to 8 micro-second. Besides being of
fundamental interest, teleportation between photonic and atomic qubits with the
direct inclusion of a readable quantum memory represents a step towards an
efficient and scalable quantum network.Comment: 19 pages 3 figures 1 tabl
Experimental demonstration of a BDCZ quantum repeater node
Quantum communication is a method that offers efficient and secure ways for
the exchange of information in a network. Large-scale quantum communication (of
the order of 100 km) has been achieved; however, serious problems occur beyond
this distance scale, mainly due to inevitable photon loss in the transmission
channel. Quantum communication eventually fails when the probability of a dark
count in the photon detectors becomes comparable to the probability that a
photon is correctly detected. To overcome this problem, Briegel, D\"{u}r, Cirac
and Zoller (BDCZ) introduced the concept of quantum repeaters, combining
entanglement swapping and quantum memory to efficiently extend the achievable
distances. Although entanglement swapping has been experimentally demonstrated,
the implementation of BDCZ quantum repeaters has proved challenging owing to
the difficulty of integrating a quantum memory. Here we realize entanglement
swapping with storage and retrieval of light, a building block of the BDCZ
quantum repeater. We follow a scheme that incorporates the strategy of BDCZ
with atomic quantum memories. Two atomic ensembles, each originally entangled
with a single emitted photon, are projected into an entangled state by
performing a joint Bell state measurement on the two single photons after they
have passed through a 300-m fibre-based communication channel. The entanglement
is stored in the atomic ensembles and later verified by converting the atomic
excitations into photons. Our method is intrinsically phase insensitive and
establishes the essential element needed to realize quantum repeaters with
stationary atomic qubits as quantum memories and flying photonic qubits as
quantum messengers.Comment: 5 pages, 4 figure
Experimental exploration of five-qubit quantum error correcting code with superconducting qubits
Quantum error correction is an essential ingredient for universal quantum
computing. Despite tremendous experimental efforts in the study of quantum
error correction, to date, there has been no demonstration in the realisation
of universal quantum error correcting code, with the subsequent verification of
all key features including the identification of an arbitrary physical error,
the capability for transversal manipulation of the logical state, and state
decoding. To address this challenge, we experimentally realise the
code, the so-called smallest perfect code that permits
corrections of generic single-qubit errors. In the experiment, having optimised
the encoding circuit, we employ an array of superconducting qubits to realise
the code for several typical logical states including the magic
state, an indispensable resource for realising non-Clifford gates. The encoded
states are prepared with an average fidelity of while with a high
fidelity of in the code space. Then, the arbitrary single-qubit
errors introduced manually are identified by measuring the stabilizers. We
further implement logical Pauli operations with a fidelity of
within the code space. Finally, we realise the decoding circuit and recover the
input state with an overall fidelity of , in total with gates.
Our work demonstrates each key aspect of the code and verifies
the viability of experimental realization of quantum error correcting codes
with superconducting qubits.Comment: 6 pages, 4 figures + Supplementary Material
Domain wall brane in squared curvature gravity
We suggest a thick braneworld model in the squared curvature gravity theory.
Despite the appearance of higher order derivatives, the localization of gravity
and various bulk matter fields is shown to be possible. The existence of the
normalizable gravitational zero mode indicates that our four-dimensional
gravity is reproduced. In order to localize the chiral fermions on the brane,
two types of coupling between the fermions and the brane forming scalar is
introduced. The first coupling leads us to a Schr\"odinger equation with a
volcano potential, and the other a P\"oschl-Teller potential. In both cases,
the zero mode exists only for the left-hand fermions. Several massive KK states
of the fermions can be trapped on the brane, either as resonant states or as
bound states.Comment: 18 pages, 5 figures and 1 table, references added, improved version
to be published in JHE
A millisecond quantum memory for scalable quantum networks
Scalable quantum information processing critically depends on the capability
of storage of a quantum state. In particular, a long-lived storable and
retrievable quantum memory for single excitations is of crucial importance to
the atomic-ensemble-based long-distance quantum communication. Although atomic
memories for classical lights and continuous variables have been demonstrated
with milliseconds storage time, there is no equal advance in the development of
quantum memory for single excitations, where only around 10 s storage time
was achieved. Here we report our experimental investigations on extending the
storage time of quantum memory for single excitations. We isolate and identify
distinct mechanisms for the decoherence of spin wave (SW) in atomic ensemble
quantum memories. By exploiting the magnetic field insensitive state, ``clock
state", and generating a long-wavelength SW to suppress the dephasing, we
succeed in extending the storage time of the quantum memory to 1 ms. Our result
represents a substantial progress towards long-distance quantum communication
and enables a realistic avenue for large-scale quantum information processing.Comment: 11pages, 4 figures, submitted for publicatio
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