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

Area of Science:

• Quantum Information Science
• Semiconductor Physics
• Photonics

Background:

• Long-distance quantum communication relies on entanglement between matter qubits and telecom-wavelength photonic qubits.
• III-V semiconductor quantum dots offer fast spin manipulation but lack demonstrated entanglement with flying photonic qubits.
• Many quantum dots emit photons at wavelengths with high fiber optic losses, hindering practical applications.

Purpose of the Study:

• To demonstrate entanglement between a single quantum dot electron spin qubit and a propagating photonic qubit.
• To overcome the wavelength limitations of quantum dot emission for long-distance quantum communication.

Main Methods:

• Utilized frequency downconversion of spontaneously emitted photons from a singly charged InAs quantum dot.
• Employed sub-10-picosecond pulses at 2.2 micrometres for frequency downconversion.
• Achieved quantum erasure of which-path information in photon energy.

Main Results:

• Successfully demonstrated entanglement between an InAs quantum-dot electron spin qubit and a photonic qubit.
• Downconverted photons to a telecommunications wavelength of 1,560 nanometres.
• Combined with high-rate indistinguishable single-photon emission, this advances quantum dot systems.

Conclusions:

• The demonstrated entanglement is a crucial step towards practical quantum repeaters and quantum teleportation.
• The frequency downconversion technique enables the use of III-V quantum dots for long-distance quantum communication.
• This work positions III-V semiconductor quantum dots as a promising platform for future quantum networks.