Researchers succeeded in executing the fastest two-qubit gate

The two-qubit gate can be reached in 6.9 nanoseconds.
Nergis Firtina
Conceptual diagram of the world’s fastest two-qubit gate.

Dr. Takafumi Tomita (IMS) 

  • A research group succeeded in executing the world's fastest two-qubit gate.
  • Quantum computers and optical tweezers were used to conduct the research.
  • It is used an ultrafast laser to manipulate cold atoms.

The world's fastest two-qubit gate has been executed in 6.5 nanoseconds by a group of researchers at the National Institutes of Natural Sciences. A research group led by graduate student Yeelai Chew, Assistant Professor Sylvain de Léséleuc, and Professor Kenji Ohmori used atoms cooled to almost absolute zero and trapped in optical tweezers separated by a micron. By manipulating the atoms with special laser light for 10 picoseconds, they executed the world's fastest two-qubit gate.

The ultrafast quantum computer, which was used by the research team to get the two-qubit gate, used ultrafast lasers to manipulate cold atoms. This computer is also expected to be a completely new quantum computer that can break the limits of superconducting and trapped-ion types, the press release revealed.

The results were published in the online edition of Nature Photonics on August 8, 2022.

What are cold-atom based quantum computers?

Cold-atom quantum computers are based on laser cooling and trapping techniques celebrated by the Nobel Prizes of 1997 (S. Chu, C. Cohen-Tannoudji and W.D. Philipps, "Cooling and trapping atoms with laser light") and 2018 (A. Ashkin, invention of the optical tweezers). Thanks to this technique, the arrays of cold atoms can be arranged in any desired way with optical tweezers, and each can be observed separately. Because atoms are natural quantum systems, they can easily store qubits, or bits of quantum information, which are artifacts of a quantum computer.

Understanding quantum gates

Quantum gates are the basic arithmetic elements that make up quantum computing. They correspond to the logic gates such as AND and OR in conventional classical computers. There are one-qubit gates that manipulate the state of a single qubit and two-qubit gates that generate quantum entanglement between two qubits.

Study abstract

Rydberg atoms, with their enormous electronic orbitals, exhibit dipole-dipole interactions reaching the gigahertz range at a distance of a micrometre, making them a prominent contender for realizing ultrafast quantum operations. However, such strong interactions between two single atoms have so far never been harnessed due to the stringent requirements on the fluctuation of the atom positions and the necessary excitation strength. Here we introduce novel techniques to explore this regime. First, we trap and cool atoms to the motional quantum ground state of holographic optical tweezers, which allows control of the inter-atomic distance down to 1.5 μm with a quantum-limited precision of 30 nm. We then use ultrashort laser pulses to excite a pair of these nearby atoms to a Rydberg state simultaneously, far beyond the Rydberg blockade regime, and perform Ramsey interferometry with attosecond precision. This allows us to induce and track an ultrafast interaction-driven energy exchange completed on nanosecond timescales—two orders of magnitude faster than in any other Rydberg experiments in the tweezers platform so far. This ultrafast coherent dynamics gives rise to a conditional phase, which is the key resource for a quantum gate, opening the path for quantum simulation and computation operating at the speed limit set by dipole–dipole interactions with this ultrafast Rydberg platform.

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