15,837 research outputs found
The entanglement beam splitter: a quantum-dot spin in a double-sided optical microcavity
We propose an entanglement beam splitter (EBS) using a quantum-dot spin in a
double-sided optical microcavity. In contrast to the conventional optical beam
splitter, the EBS can directly split a photon-spin product state into two
constituent entangled states via transmission and reflection with high fidelity
and high efficiency (up to 100 percent). This device is based on giant optical
circular birefringence induced by a single spin as a result of cavity quantum
electrodynamics and the spin selection rule of trion transition (Pauli
blocking). The EBS is robust and it is immune to the fine structure splitting
in a realistic quantum dot. This quantum device can be used for
deterministically creating photon-spin, photon-photon and spin-spin
entanglement as well as a single-shot quantum non-demolition measurement of a
single spin. Therefore, the EBS can find wide applications in quantum
information science and technology.Comment: 7 pages, 5 figure
Strain-tunable entangled-light-emitting diodes with high yield and fast operation speed
Triggered sources of entangled photons play crucial roles in almost any
existing protocol of quantum information science. The possibility to generate
these non-classical states of light with high speed and using electrical pulses
could revolutionize the field. Entangled-light-emitting-diodes (ELEDs) based on
semiconductor quantum dots (QDs) are at present the only devices that can
address this task 5. However, ELEDs are plagued by a source of randomness that
hampers their practical exploitation in the foreseen applications: the very low
probability (~10-2) of finding QDs with sufficiently small
fine-structure-splitting for entangled-photon-generation. Here, we overcome
this hurdle by introducing the first strain-tunable ELEDs (S-ELEDs) that
exploit piezoelectric-induced strains to tune QDs for
entangled-photon-generation. We demonstrate that up to 30% of the QDs in
S-ELEDs emit polarization-entangled photon pairs with entanglement-fidelities
as high as f+ = 0.83(5). Driven at the highest operation speed of 400 MHz ever
reported so far, S-ELEDs emerge as unique devices for high-data rate
entangled-photon applications.Comment: 28 pages in total, including supplementary information. 5 figure
Oscillating photonic Bell state from a semiconductor quantum dot for quantum key distribution
An on-demand source of bright entangled photon pairs is desirable for quantum
key distribution (QKD) and quantum repeaters. The leading candidate to generate
entangled photon pairs is based on spontaneous parametric down-conversion
(SPDC) in a non-linear crystal. However, there exists a fundamental trade-off
between entanglement fidelity and efficiency in SPDC sources due to multiphoton
emission at high brightness, which limits the pair extraction efficiency to
0.1% when operating at near-unity fidelity. Quantum dots in photonic
nanostructures can in principle overcome this trade-off; however, the quantum
dots that have achieved entanglement fidelities on par with SPDC sources (99%)
have poor pair extraction efficiencies of 0.01%. Here, we demonstrate a 65-fold
increase in the pair extraction efficiency compared to quantum dots with
equivalent peak fidelity from an InAsP quantum dot in a photonic nanowire
waveguide. We measure a raw peak concurrence and fidelity of 95.3% 0.5%
and 97.5% 0.8%, respectively. Finally, we show that an oscillating
two-photon Bell state generated by a semiconductor quantum dot can be utilized
to establish a secure key for QKD, alleviating the need to remove the quantum
dot energy splitting of the intermediate exciton states in the
biexciton-exciton cascade.Comment: 24 pages (7 main body, excluding references plus 14 supplemental
information) and 4 main body figure
The Quantum Reverse Shannon Theorem based on One-Shot Information Theory
The Quantum Reverse Shannon Theorem states that any quantum channel can be
simulated by an unlimited amount of shared entanglement and an amount of
classical communication equal to the channel's entanglement assisted classical
capacity. In this paper, we provide a new proof of this theorem, which has
previously been proved by Bennett, Devetak, Harrow, Shor, and Winter. Our proof
has a clear structure being based on two recent information-theoretic results:
one-shot Quantum State Merging and the Post-Selection Technique for quantum
channels.Comment: 30 pages, 4 figures, published versio
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