Photons Pave the Way for Advances in Quantum Computing

Quantum physics holds the hope for computers with better speed and greater capabilities. The current limitation in the development of quantum computing is the need for quantum equivalents of logical gates.

Researchers at the University of Cambridge and Toshiba Research Europe have made a significant progress in this direction by developing a quantum controlled NOT gate labeled CNOT. Computers as we know them today, compute by means of binary digits or bits which essentially consist of ones and zeroes. Logical gates help switch the state of a bit between 1 and 0. Quantum computers operate by means of quantum bits or qubits which have a unique property of existing in both states simultaneously. Quantum computing can be carried out with just two basic components: a CNOT gate and a qubit gate.

A CNOT gate requires two qubits for its functioning. One is a target qubit and the other is a control qubit. The target qubit is subject to the NOT operation depending on the state of the control qubit. Photons represent the qubits. The photons are made to go through micro cracks in semiconductors, known as waveguides to perform a calculation. Generation of these photons is central to the operation of the quantum CNOT gate. This has been achieved by the researchers by embedding a quantum dot in a silicon pillar’s micro cavity which serves to speed up the emission of photons. The photon emission takes place when electrons in the quantum dot fall back to their original state from a state of higher energy they are excited to when subject to a laser pulse.

The next milestone in the ongoing research is to incorporate all the components into a single device.