Leo Yu

Quantum-dot spin–photon entanglement via frequency downconversion to telecom wavelength

Long-distance quantum teleportation and quantum repeater technologies require entanglement between a single matter quantum bit (qubit) and a telecommunications (telecom)-wavelength photonic qubit. Electron spins in III–V semiconductor quantum dots are among the matter qubits that allow for the fastest spin manipulation and photon emission, but entanglement between a single quantum-dot spin qubit and a flying (propagating) photonic qubit has yet to be demonstrated. Moreover, many quantum dots emit single photons at visible to near-infrared wavelengths, where silica fibre losses are so high that long-distance quantum communication protocols become difficult to implement. Here we demonstrate entanglement between an InAs quantum-dot electron spin qubit and a photonic qubit, by frequency downconversion of a spontaneously emitted photon from a singly charged quantum dot to a wavelength of 1,560 nanometres. The use of sub-10-picosecond pulses at a wavelength of 2.2 micrometres in the frequency downconversion process provides the necessary quantum erasure to eliminate which-path information in the photon energy. Together with previously demonstrated indistinguishable single-photon emission at high repetition rates, the present technique advances the III–V semiconductor quantum-dot spin system as a promising platform for long-distance quantum communication.

Downconversion quantum interface for a single quantum dot spin and 1550-nm single-photon channel.

We report an ultrafast downconversion quantum interface, where 910-nm single photons from a quantum dot are downconverted to the 1.5-μm telecom band with sub-10 picosecond pulses at 2.2-μm, enabling the demonstration of quantum-dot spin-photon entanglement.

Possible origin of the nonmonotonic doping dependence of the in-plane resistivity anisotropy of Ba(Fe1−xTx)2As2 (T = Co, Ni and Cu)

The in-plane resistivity anisotropy has been measured for detwinned single crystals of Ba(Fe

Cascaded frequency upconversion for high-speed single-photon detection at 1550 nm

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Complete tomography of a high-fidelity solid-state entangled spin–photon qubit pair

Ni

Two-photon interference at telecom wavelengths for time-bin-encoded single photons from quantum-dot spin qubits

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Background-free quantum frequency downconversion for two-photon interference of heterogeneous photon sources

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Ultrafast downconversion quantum interface for a single quantum dot spin and 1550-nm single-photon channel

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Single spins in semiconductor quantum dot microcavities

As

Ultrafast optical control of individual electron and hole spin qubits: entanglement between a single quantum dot electron spin and a downconverted 1560-nm single photon

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