New device creates entangled photons that span the traditional telecommunications spectrum, making it appealing for multi-channel quantum communication and more powerful quantum computers. Credit: Michael Kues, Institut National de la Recherche Scientifique (INRS), University of Quebec, Canada
Discovery is a significant step toward multi-channel quantum communication and higher capacity quantum computers. An international team has built a chip that generates multiple frequencies from a robust quantum system that produces time-bin entangled photons. In contrast to other quantum state realizations, entangled photons don’t need bulky equipment to keep them in their quantum state, and they can transmit quantum information across long distances. The new device creates entangled photons that span the traditional telecommunications spectrum, making it appealing for multi-channel quantum communication and more powerful quantum computers.
“The advantages of our chip are that it’s compact and cheap. It’s also unique that it operates on multiple channels,” said Michael Kues,INRS, Uni of Quebec, Canada.
The basis of quantum communications and computing lies in qubits, the quantum equivalent of classical bits. Instead of representing a one or a zero, qubits can exhibit an unusual property called superposition to represent both numbers simultaneously. Entanglement links particles so that measurements on one instantaneously affect the other.
Kues and his colleagues used photons to realize their qubits and entangled them by sending 2 short laser pulses through an interferometer, a device that directs light beams along different paths and then recombines them, to generate double pulses. To generate multiple frequencies, Kres et al sent the pulses through a microring resonator. The resonator generates photon pairs on a series of discrete frequencies, using spontaneous form-wave mixing, thus creating a frequency comb.
The interferometer the team used has one long arm and one short arm, and when a single photon comes out of the system, it is in a superposition of time states, as if it traveled through both the long arm and the short arm simultaneously. Time-bin entanglement is a particularly robust form of photon entanglement. Photons can also have their polarization entangled, but waveguides and other types of optical equipment may alter polarization states.
Other research groups have generated time-bin entangled photons, but Kues and his colleagues are the first to create photons with multiple frequencies using the same chip. This feature can enable multiplexed and multi-channel quantum communications and increased quantum computation information capacity.
The chip could improve quantum key distribution, a process that lets two parties share a secret key to encrypt messages with theoretically unbreakable security. It could also serve as a component of a future quantum computer.
“In the future you may have a computer with both quantum and classical capabilities. The quantum part would only be used to solve specific problems that are difficult for classical computers,” said Roberto Morandotti, INRS. Before quantum computers reach a desktop near you, they need to be scaled down, in terms of size, and scaled up, in terms of computing power. Morandotti, Kues and colleagues think their chip is a step in the right direction.
The team is currently working to integrate the lasers, interferometer, and microring resonator of the device into a standard photonic chip, to build logic gates for quantum state manipulation, and to increase the degree of entanglement, which is a measure of the strength of the link between particles. http://www.cleoconference.org/home/news-and-press/cleo-press-releases/researchers-create-a-first-frequency-comb-of-time
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