On-chip quantum buffer realized

November 13, 2013 in Physics / Quantum Physics
Photonic quantum computer based on integrated quantum optical circuits

Nippon Telegraph and Telephone Corp. has realized a quantum buffer integrated on an optical waveguide. The buffer is based on the "slow light effect", where the propagation speed of a pulsed light in a special optical waveguide slows significantly compared with the speed of light in vacuum.

The buffer facilitates the precise synchronization of photons in two quantum interference experiments needed for realizing , and thus moves us forward in our goal of realizing quantum computers based on photonic quantum bit (qubit).

This result will be published in the UK science journal Nature Communications on November 12, 2013.

There are many schemes for the physical realization of a qubit that can be used for , including superconducting devices, semiconductor nanostructures, atoms and photons. Among them, a photon can be used as a stable qubit, since a photon rarely is affected by noise in environment.

To construct a quantum computer, we need "two-qubit quantum gates" where logic operations to two qubits are undertaken by interacting them. In the case of photonic qubits, it is well known that such gates are constructed using the quantum interference of photons. Recently, intensive research has been undertaken to build integrated quantum optical circuits in order to enable and realize large-scale photonic quantum computers.

For the realization of quantum gates based on photon interference, we need to synchronize the arrival times of photons at the photonic quantum circuits very precisely. A quantum buffer, where a photon is stored while faithfully preserving its quantum state, can facilitate the synchronization of the photons and thus achieve a quantum gate operation.

Coupled resonator optical waveguide(CROW) based on silicon photonic crystal

We have realized a quantum buffer by using the "slow light effect" (where the speed of pulsed light is significantly reduced compared with the speed of light in vacuum) in coupled nanocavities fabricated utilizing our silicon photonic crystal fabrication technology.

We undertook our experiments described below to evaluate the performance of these coupled nanocavities as a quantum buffer. As a result, we successfully demonstrated that the buffer could slow down the speed of pulsed photons to 1/60 of the speed of light in vacuum while faithfully preserving its quantum state. This result confirmed that the developed device could be used as a quantum buffer integrated on chip.

The use of the quantum buffer will facilitate the synchronization of photons in various patterns of optical circuits, and thus is expected to increase the integration level of the quantum optical circuit. In addition, the tunability of our buffer will help realize the reconfigurable quantum optical circuit.

Setup for measuring single photon delay and entanglement preservation by coupled nanocavities

Technical Features:

We will develop high-efficiency single photon detector integrated on a chip. Then, we will build an integrated quantum optical circuit where components such as photon sources, detectors and buffers are implemented on a chip for realizing photonic quantum computers.

More information: Hiroki Takesue, Nobuyuki Matsuda, Eiichi Kuramochi, William J. Munro, and Masaya Notomi, "An on-chip coupled resonator optical waveguide single-photon buffer, "Nature Communications (2013)

Provided by NTT

"On-chip quantum buffer realized" November 13, 2013 https://phys.org/news/2013-11-on-chip-quantum-buffer.html