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Quantum Relay

Entanglement

Entangled particles have interconnected properties, so that measurement of one changes the other, even if it is far away. At Toshiba, we are developing sources of entangled light particles, known as photons. The photons are entangled in their polarisation, which is the orientation of the electromagnetic field. Measurement of the polarisation of a photon gives a random result, that will cause the paired photon to have the same polarisation.

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Quantum Teleportation

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Quantum teleportation destroys quantum information so it can appear elsewhere. Its name was inspired by similarities with teleportation in science fiction, but quantum teleportation doesn’t break any laws of physics.

Physics dictates that the qubits that carry quantum information cannot be copied, so teleportation offers a way to move quantum data around networks, or quantum processors.

To teleport quantum information, we need to share a pair of entangled qubits between a sender and receiver. One of the entangled qubits is destroyed, together with the input qubit, which teleports the input data onto the receivers remaining qubit.

The destruction of the qubits reveals no information about the information encoded on the input, but does indicate if any adjustment to the target qubit is necessary, so teleportation is not faster than light speed.

Entangled LED

Generation of entangled light can be achieved in several ways, but at Toshiba we focus on technology compatible with conventional semiconductor opto-electronics. We introduced the world’s first entangled light emitting diode (ELED), which generates pairs of entangled photons in a semiconductor device similar the humble LEDs found in low energy lighting and in consumer electronics.

The device is based on tiny nano-metre scale quantum dots made from the semiconductor indium arsenide (InAs), within an resonant cavity LED. Applying an electrical current causes charge to accumulate within the quantum dots, which then emit pairs of entangled photons. In the image, each of the bright spots corresponds to such a quantum dot, and light from just one of which is collected using a microscope lens for applications.

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Quantum Relay

Quantum bits cannot be copied, which is great for security but a headache for routing quantum keys and data across networks. One solution is to use a quantum relay, which used entangled photons and teleportation to destroy the input qubits so they can be transferred to another part of the network. We develop quantum relay systems operating over optical fibres. The input qubits are generated by lasers, and destroyed by joint measurement with an entangled photon from and LED. This process, known as a Bell State Measurement (BSM) teleports the qubit to the output, where it can be detected with a receiver.

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