Superconducting Quantum Bit Light-Conducting Fiber

NIST physicists measured and managed a superconducting quantum bit (qubit) utilizing light-conducting fiber (indicated by white arrow) as an alternative of steel electrical cables just like the 14 proven right here inside a cryostat. Through the use of fiber, researchers might doubtlessly pack 1,000,000 qubits right into a quantum laptop somewhat than just some thousand. Credit score: F. Lecocq/NIST

Optical Fiber Might Increase Energy of Superconducting Quantum Computer systems

The key to constructing superconducting quantum computer systems with huge processing energy could also be an atypical telecommunications know-how — optical fiber. 

Physicists on the Nationwide Institute of Requirements and Expertise (NIST) have measured and managed a superconducting quantum bit (qubit) utilizing light-conducting fiber as an alternative of steel electrical wires, paving the way in which to packing 1,000,000 qubits right into a quantum laptop somewhat than just some thousand. The demonstration is described within the March 25 challenge of Nature.

Superconducting circuits are a number one know-how for making quantum computer systems as a result of they’re dependable and simply mass produced. However these circuits should function at cryogenic temperatures, and schemes for wiring them to room-temperature electronics are advanced and vulnerable to overheating the qubits. A common quantum laptop, able to fixing any kind of downside, is anticipated to want about 1 million qubits. Typical cryostats — supercold dilution fridges — with steel wiring can solely assist 1000’s on the most.

Optical fiber, the spine of telecommunications networks, has a glass or plastic core that may carry a excessive quantity of sunshine indicators with out conducting warmth. However superconducting quantum computer systems use microwave pulses to retailer and course of data. So the sunshine must be transformed exactly to microwaves. 

To unravel this downside, NIST researchers mixed the fiber with a couple of different normal parts that convert, convey and measure gentle on the stage of single particles, or photons, which might then be simply transformed into microwaves. The system labored in addition to steel wiring and maintained the qubit’s fragile quantum states.

“I feel this advance could have excessive affect as a result of it combines two completely totally different applied sciences, photonics and superconducting qubits, to resolve an important downside,” NIST physicist John Teufel stated. “Optical fiber may also carry much more knowledge in a a lot smaller quantity than typical cable.”

Usually, researchers generate microwave pulses at room temperature after which ship them by way of coaxial steel cables to cryogenically maintained superconducting qubits. The brand new NIST setup used an optical fiber as an alternative of steel to information gentle indicators to cryogenic photodetectors that transformed indicators again to microwaves and delivered them to the qubit. For experimental comparability functions, microwaves could possibly be routed to the qubit by way of both the photonic hyperlink or an everyday coaxial line.

The “transmon” qubit used within the fiber experiment was a tool often called a Josephson junction embedded in a three-dimensional reservoir or cavity. This junction consists of two superconducting metals separated by an insulator. Underneath sure circumstances {an electrical} present can cross the junction and will oscillate backwards and forwards. By making use of a sure microwave frequency, researchers can drive the qubit between low-energy and excited states (1 or 0 in digital computing). These states are primarily based on the variety of Cooper pairs — certain pairs of electrons with reverse properties — which have “tunneled” throughout the junction. 

The NIST staff carried out two varieties of experiments, utilizing the photonic hyperlink to generate microwave pulses that both measured or managed the quantum state of the qubit. The strategy relies on two relationships: The frequency at which microwaves naturally bounce backwards and forwards within the cavity, known as the resonance frequency, will depend on the qubit state. And the frequency at which the qubit switches states will depend on the variety of photons within the cavity.

Researchers usually began the experiments with a microwave generator. To regulate the qubit’s quantum state, units known as electro-optic modulators transformed microwaves to larger optical frequencies. These gentle indicators streamed by way of optical fiber from room temperature to 4 kelvins (minus 269 C or minus 452 F) down to twenty millikelvins (thousandths of a kelvin), the place they landed in high-speed semiconductor photodetectors, which transformed the sunshine indicators again to microwaves that had been then despatched to the quantum circuit.

In these experiments, researchers despatched indicators to the qubit at its pure resonance frequency, to place it into the specified quantum state. The qubit oscillated between its floor and excited states when there was satisfactory laser energy. 

To measure the qubit’s state, researchers used an infrared laser to launch gentle at a particular energy stage by way of the modulators, fiber and photodetectors to measure the cavity’s resonance frequency.

Researchers first began the qubit oscillating, with the laser energy suppressed, after which used the photonic hyperlink to ship a weak microwave pulse to the cavity. The cavity frequency precisely indicated the qubit’s state 98% of the time, the identical accuracy as obtained utilizing the common coaxial line.

The researchers envision a quantum processor by which gentle in optical fibers transmits indicators to and from the qubits, with every fiber having the capability to hold 1000’s of indicators to and from the qubit.

Reference: “Management and readout of a superconducting qubit utilizing a photonic hyperlink” by F. Lecocq, F. Quinlan, Okay. Cicak, J. Aumentado, S. A. Diddams and J. D. Teufel, 24 March 2021, Nature.
DOI: 10.1038/s41586-021-03268-x

By Rana

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