Integrated optical quantum memory for ultra-fast information processing

The development of quantum computers is fast-becoming a key focus within the machine-learning, big-data, finance, security and healthcare industries, amongst others. Their applications are wide-ranging and have capabilities far beyond those of classical computers, and a key component essential to their success is the quantum memory technology within them.

There has not been a practical implementation of a quantum memory to date, due to problems with storage and retrieval efficiency, low storage bandwidth and the presence of unwanted noise. New technology from the University of Oxford overcomes this problem and is easily integrated into current fibre-based photonic networks. It can operate at various wavelengths, including telecom in principle.

The Oxford technology could be used for a multitude of applications, including those in quantum metrology, communication and computing.

This patented Quantum memory works at the interface between light and matter allowing for the storage and retrieval of photonic quantum information, analogous to the memory in a normal computer. The quantum memory allows a system to store quantum information without measuring it; once measured, the information ceases to exist as a quantum state and becomes classical information. This memory has applications in the world of both quantum and classical computing.

Oxford University academics have developed an integrated, fibre-based quantum memory, which allows for the on-demand storage and retrieval of broadband (>1GHz) pulses of light. This memory can be used as an enabling component of linear optical quantum computing networks and would have broad applications in quantum metrology, communication and computing.

Currently, there has not been a practical implementation of a quantum memory, due to problems with storage/ retrieval efficiency, low storage bandwidth and the presence of unwanted noise. The proposed technology, which is based on a novel quantum memory protocol, overcomes all of these problems, as it is inherently noise-free and broadband.

By using a coherent two-photon absorption process, where two photons of different wavelengths are sent into a storage medium (e.g. rubidium gas), there is no cross-coupling of the light fields that could lead to unwanted noise. The technology has been demonstrated at 780nm in rubidium and 852nm in cesium, and in principle could also be applied to telecom wavelengths.

The technology can be implemented in a gas-filled hollow-core photonic crystal fibre, which is tapered and spliced to single-mode fibres at both ends, creating a microcell. This geometry increases memory efficiency and lowers the power requirement of the memory, making it scalable and integratable with fibre-based photonic networks.

Both quantum and non-quantum applications

The quantum device is used for storage and retrieval of both quantum and classical light pulses and could be used as a time-frequency mode converter, and in principle could also be used as a dynamically reconfigurable delay line or a rapidly reconfigurable beam splitter for quantum or classical light pulses.

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