546 research outputs found
High-rate, high-fidelity entanglement of qubits across an elementary quantum network
We demonstrate remote entanglement of trapped-ion qubits via a
quantum-optical fiber link with fidelity and rate approaching those of local
operations. Two Sr qubits are entangled via the polarization
degree of freedom of two photons which are coupled by high-numerical-aperture
lenses into single-mode optical fibers and interfere on a beamsplitter. A novel
geometry allows high-efficiency photon collection while maintaining unit
fidelity for ion-photon entanglement. We generate remote Bell pairs with
fidelity at an average rate (success
probability ).Comment: v2 updated to include responses to reviewers, as published in PR
Generating remote entanglement via disentangling operations
Shared entanglement between spatially separated systems is an essential
resource for quantum information processing including long-distance quantum
cryptography and teleportation. While purification protocols for mixed
distributed entangled quantum states exist, it is not clear how to optimally
distribute entanglement to remote locations. Here, we describe a deterministic
protocol for generating a maximally entangled state between remote locations
that only uses local operations on qubits, and requires no classical
communication between the separated parties. The procedure may provide
protection from decoherence before the entanglement is "activated," and could
be useful for quantum key distribution.Comment: 6 pages, 3 figure
Quantum Repeaters using Coherent-State Communication
We investigate quantum repeater protocols based upon atomic
qubit-entanglement distribution through optical coherent-state communication.
Various measurement schemes for an optical mode entangled with two spatially
separated atomic qubits are considered in order to nonlocally prepare
conditional two-qubit entangled states. In particular, generalized measurements
for unambiguous state discrimination enable one to completely eliminate
spin-flip errors in the resulting qubit states, as they would occur in a
homodyne-based scheme due to the finite overlap of the optical states in phase
space. As a result, by using weaker coherent states, high initial fidelities
can still be achieved for larger repeater spacing, at the expense of lower
entanglement generation rates. In this regime, the coherent-state-based
protocols start resembling single-photon-based repeater schemes.Comment: 11 pages, 8 figure
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