Controlled Rephasing of Single Collective Spin Excitations in a Cold Atomic Quantum Memory

Area of Science:

• Quantum optics
• Atomic physics
• Quantum information science

Background:

• Controlling quantum states is crucial for quantum technologies.
• Inhomogeneous dephasing in atomic ensembles degrades quantum information.
• Collective atomic spin excitations (spin waves) are promising quantum states.

Purpose of the Study:

• To demonstrate active control of dephasing and rephasing for single spin waves.
• To preserve the single-photon nature of retrieved photons.
• To enable temporal multiplexing for quantum repeaters.

Main Methods:

• Utilizing cold 87Rb atoms as a quantum memory.
• Employing a reversible external magnetic field gradient to control dephasing.
• Creating single spin waves via spontaneous Raman scattering.
• Experimentally verifying photon properties and temporal control.

Main Results:

• Active rephasing successfully preserved the single-photon nature of retrieved photons.
• Demonstrated control over inhomogeneous dephasing and rephasing of spin waves.
• Achieved the creation of time-separated spin waves within a single atomic ensemble.
• Enabled selective read-out of these time-separated spin waves.

Conclusions:

• Active control of dephasing is a viable technique for quantum memories.
• This method is a key step towards building temporally multiplexed quantum repeater nodes.
• The demonstrated control enhances the potential for scalable quantum communication networks.