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Posted: May 18th, 2012 Quantum computing: The light at the end of the tunnel may be asingle photon ( Nanowerk News ) Quantum physics promises faster and more powerful computers, butquantum versions of basic logic functions are still needed to bringthis technology to fruition. Researchers from the University ofCambridge and Toshiba Research Europe Ltd. have taken one steptoward this goal by creating an all-semiconductor quantum logicgate, a controlled-NOT (CNOT) gate. They achieved this breakthroughby coaxing nanodots to emit single photons of light on demand. "The ability to produce a photon in a very precise state is ofcentral importance," said Matthew Pooley of Cambridge Universityand co-author of a study accepted for publication in the AmericanInstitute of Physics' (AIP) journal Applied Physics Letters ("Controlled-NOT gate operating with single photons")."We used standard semiconductor technology to create single quantumdots that could emit individual photons with very precisecharacteristics." These photons could then be paired up to zipthrough a waveguide, essentially a tiny track on a semiconductor,and perform a basic quantum calculation. Classical computers perform calculations by manipulating binarybits, the familiar zeros and ones of the digital age. A quantumcomputer instead uses quantum bits, or qubits. Because of theirweird quantum properties, a qubit can represent a zero, one, orboth simultaneously, producing a much more powerful computingtechnology. To function, a quantum computer needs two basicelements: a single qubit gate and a controlled-NOT gate. A gate issimply a component that manipulates the state of a qubit. Anyquantum operation can be performed with a combination of these twogates. To produce the all-important initial photon, the researchersembedded a quantum dot in a microcavity on a pillar of silicon. Alaser pulse then excited one of the electrons in the quantum dot,which emitted a single photon when the electron returned to itsresting state. The pillar microcavity helped to speed up thisprocess, reducing the time it took to emit a photon. It also madethe emitted photons nearly indistinguishable, which is essentialbecause it takes two photons, or qubits, to perform the CNOTfunction: one qubit is the "control qubit" and the other is the"target qubit." The NOT operation is performed on the target qubit,but the result is conditional on the state of the control qubit.The ability for qubits to interact with each other in this way iscrucial to building a quantum computer. The next step is to integrate the components into a single device,drastically reducing the size of the technology. "Also, we use justone photon source to generate both the photons used for thetwo-photon input state. An obvious next step would be to use twosynchronized photon sources to create the input state," saidPooley. I am an expert from fiber-opticcomponents.com, while we provides the quality product, such as Fiber Optic Adaptor , Fiber Media Converters Manufacturer, Fiber Optic Patch Cord,and more.
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