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REHOVOT, Israel, September 5, 2018 – The quantum optics laboratory of the Weizmann Institute of Science has created a logical gate in which a photon and an atom can automatically exchange the information they carry. This breakthrough could help develop quantum computers for practical use.
Although small-scale quantum computers have been demonstrated, the challenge of increasing these computers to millions of qubits remains. Indeed, for qubits to exist in a state of quantum superposition, they must be isolated; and at the same time, they must interact and communicate with other qubits. Quantum superposition – a phenomenon in which qubits exist in several states at once – is what gives qubits an advantage over conventional computing, since a computer composed of qubits could perform many calculations in parallel.
A quantum gate between atoms and photons can help increase quantum computers. With the kind permission of the Weizmann Institute of Sciences.
Weizmann's team is studying a possible solution to scale up quantum computers – isolated modules with a small number of qubits that would communicate with each other through optical links. The information stored in a hardware qubit (a single atom or ion) would be transferred to a flying qubit (a single photon). The photon would be sent via fiber optics to a remote hardware qubit, and would transfer information to that qubit without leaving anything in the environment to decrypt the information.
The challenge in creating such a system is that single photons carry extremely low amounts of energy and that tiny systems including material qubits generally do not interact strongly with such low light.
The team has set up an experiment coupling single atoms to unique silica resonators at the micron scale on chips. The photons are sent directly to these resonators via special optical fibers, in order to create a logic gate in which information is exchanged between a flying qubit and a hardware qubit.
Teacher. Barak Dayan and his quantum optics lab group, (l-r): Gabi Guendelman, Dor Korn, Niv Drucker, Tal Ohana, prof. Barak Dayan, Moran Netser, Ziva Aqua, Ori Mor and Dr. Adrien Borne. With the kind permission of the Weizmann Institute of Sciences.
"The photon carries a qubit, and the atom is a second qubit," said Professor Barak Dayan. "Whenever the photon and the atom meet, they exchange the qubits between them automatically and simultaneously, and the photon continues its path with the new bit of information. In quantum mechanics, in which information can not be copied or erased, this exchange of information is in fact the basic unit of reading and writing – the "native" door of quantum communication.
This kind of logic gate – called SWAP gate – could be used to exchange qubits both in and between quantum computers. Since this gate does not require external control fields or management systems, it could allow the construction of the quantum equivalent of very large scale integration networks (VLSI), according to the researchers. .
"The SWAP gate that we have demonstrated is applicable to photonic communication between all types of matter-based qubits, not just atoms," Dayan said. "We therefore believe that it will become an essential part of the next generation of quantum computing systems."
The search was published in Physics of nature (doi: 10.1038 / s41567-018-0241-6).
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