Protecting a quantum memory for a photonic polarization qubit in a cold atomic ensemble by dynamical decoupling

Area of Science:

• Quantum Information Science
• Atomic, Molecular, and Optical Physics
• Quantum Computing

Background:

• Photonic polarization qubits (PPQ) are fundamental units for quantum information processing.
• Quantum state decoherence limits the storage time of qubits.
• Dynamical decoupling (DD) techniques can suppress decoherence.

Purpose of the Study:

• To experimentally demonstrate the storage of a photonic polarization qubit (PPQ) protected by dynamical decoupling (DD).
• To investigate the effectiveness of Carr-Purcell-Meiboom-Gill (CPMG) DD sequences in suppressing decoherence of spin-wave superpositions.
• To enhance the storage time of quantum information encoded in photonic qubits.

Main Methods:

• Storing PPQ states as a superposition of two spin waves using electromagnetically-induced-transparency (EIT).
• Applying Carr-Purcell-Meiboom-Gill (CPMG) DD sequences to the spin-wave superposition.
• Measuring quantum process fidelity over time to quantify storage performance.

Main Results:

• Quantum process fidelity remained above 0.8 for storage times up to 800 μs.
• The storage time was extended by 3.4 times compared to storage without CPMG sequences (~180 μs).
• DD effectively suppressed decoherence in the spin-wave superposition encoding the qubit.

Conclusions:

• Dynamical decoupling, specifically CPMG sequences, significantly enhances the storage time of photonic polarization qubits.
• This experimental demonstration is a critical advancement towards robust quantum memory for single-photon qubits.
• The findings pave the way for developing more reliable quantum communication and computation systems.