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Advancements in control techniques break precedents, offering unprecedented accuracy in superconducting qubit operations.

MIT scientists in the Departments of Physics and Electrical Engineering and Computer Science, along with the Research Laboratory of Electronics, improved a quantum bit known as fluxonium, achieving an unprecedented single-qubit fidelity of 99.998% using two novel control methods.

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MIT scientists, hailing from the Physics and EECS departments, along with the Research Laboratory...
MIT scientists, hailing from the Physics and EECS departments, along with the Research Laboratory of Electronics, utilized a superconducting qubit named fluxonium. They implemented two innovative control methods, setting a new standard for single-qubit fidelity at an impressive 99.998%.

Advancements in control techniques break precedents, offering unprecedented accuracy in superconducting qubit operations.

Quantum computers, using the quirky rules of quantum mechanics, can theoretically solve complex problems at breakneck speeds compared to classical computers. But they come with their own set of challenges, one being the sensitivity of qubits to background noise and control flaws, which result in errors during quantum operations. To tackle this issue and improve the situation, researchers at MIT have developed two new control techniques using a type of superconducting qubit known as fluxonium. Their work has achieved a record-breaking single-qubit fidelity of 99.998 percent.

One major issue with quantum computing is decoherence, where qubits lose their quantum information. High gate fidelities are essential to implement sustained computation through quantum error-correcting protocols. MIT researchers are working on making quantum gates as swift as possible to minimize the impact of decoherence, but this can lead to another type of error called counter-rotating errors due to the electromagnetic waves controlling the qubits.

To tackle the pesky counter-rotating errors, Leon Ding, a former MIT researcher, came up with an idea to utilize circularly polarized microwave drives, much like circularly polarized light. By controlling the relative phase of charge and flux drives of a superconducting qubit, this circularly polarized drive would ideally be immune to counter-rotating errors. However, the fidelities achieved with circularly polarized drives weren't as high as expected, prompting the team to brainstorm solutions.

Rower, the lead author, says, "We stumbled upon a beautifully simple idea. If we applied pulses at exactly the right times, we should be able to make counter-rotating errors consistent from pulse-to-pulse, making them correctable. Even better, they would be automatically accounted for with our usual Rabi gate calibrations!"

This idea was dubbed "commensurate pulses," as the pulses needed to be applied at times commensurate with intervals determined by the qubit frequency through its inverse, the time period. Unlike circularly polarized microwaves that require additional calibration, commensurate pulses are defined by timing constraints alone. Rower states, "I had much fun developing the commensurate technique. It was simple, we understood why it worked so well, and it should be portable to any qubit suffering from counter-rotating errors!"

With further research, the team hopes to push the boundaries and create even faster and higher-fidelity gates. This breakthrough showcases the promise of fluxonium as a viable qubit platform for quantum computing. Fluxonium qubits are a type of superconducting qubit made up of a capacitor, Josephson junction, and a superinductor, which helps protect the qubit from environmental noise. Despite having higher coherence, fluxonium has a lower qubit frequency that is generally associated with proportionally longer gates.

Ding adds, "Our experiments really show that fluxonium is a qubit that supports both interesting physical explorations and also absolutely delivers in terms of engineering performance."

In their paper, the researchers also explore the interplay between platform-independent control techniques and the underlying physics, demonstrating "commensurate" non-adiabatic control that goes beyond the standard "rotating wave approximation" of standard Rabi approaches. Furthermore, they demonstrate it using an analog to circularly polarized light, resulting in a beautiful connection with counter-rotating dynamics.

This collaboration between physics and electrical engineering has resulted in higher performance qubits and brings us one step closer to fault-tolerant quantum computing. With Google's recent announcement of their Willow quantum chip demonstrating quantum error correction beyond threshold for the first time, this work couldn't be more timely. Higher-performant qubits will lead to lower overhead requirements for implementing error correction in quantum computers.

In layman's terms, the team has devised two new techniques to make qubits faster and more accurate, thereby reducing errors during quantum operations. These techniques, called commensurate pulses and circularly polarized microwaves, have great potential for improved single-qubit fidelity and could lead to advancements in the field of quantum computing.

  1. Quantum computers, in spite of their potential to solve complex problems quickly, face challenges, such as the sensitivity of qubits to background noise and control flaws, leading to errors during quantum operations.
  2. Researchers at MIT have developed two new control techniques using a type of superconducting qubit known as fluxonium to tackle these issues, achieving a record-breaking single-qubit fidelity of 99.998 percent.
  3. One of the major issues with quantum computing is decoherence, where qubits lose their quantum information, making high gate fidelities essential for implementing sustained computation through quantum error-correcting protocols.
  4. The team is working on making quantum gates as swift as possible to minimize the impact of decoherence, but this can lead to another type of error called counter-rotating errors due to the electromagnetic waves controlling the qubits.
  5. To tackle the counter-rotating errors, the team used circularly polarized microwave drives, but the fidelities achieved weren't as high as expected, prompting them to come up with another solution.
  6. The solution, called "commensurate pulses," involves applying pulses at exactly the right times to make counter-rotating errors consistent and correctable, with the potential to lead to advancements in the field of quantum computing.
  7. This collaboration between physics and electrical engineering has resulted in higher performance qubits and brought us one step closer to fault-tolerant quantum computing, with Google's recent announcement of their Willow quantum chip demonstrating quantum error correction beyond threshold for the first time.
  8. In layman's terms, the team has devised two new techniques to make qubits faster and more accurate, thereby reducing errors during quantum operations, with the potential to lead to significant advancements in the field of quantum computing.

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