Improved control circuits for quantum computers that reduce costs and increase performance.

Gustavo Cancelo led a team of Fermilab engineers to create a new compact electronics board: It has the capabilities of an entire rack of equipment that is compatible with many designs of superconducting qubits at a fraction of the cost. Credit: Ryan Postel, Fermilab

The challenge of bridging the communication gap between the classical and quantum worlds is unexpectedly great when constructing a next-generation quantum computer. Existing systems are laborious and expensive for translating between the human operator and the quantum computer’s languages, which are required for such machines.

Researchers at Fermi National Accelerator Laboratory in the US have developed a new control and readout system, known as QICK, that has proven to significantly boost quantum computer performance while reducing the cost of control equipment.

Quantum Instrument Control Kit development is an excellent example of US investment in joint quantum technology research with partnerships between industry, academia and government to accelerate pre-competitive quantum research and development technologies, said Harriet Kung, DOE deputy director for science programmes in the Office of Science and acting associate director of science for high-energy physics. Kung.

In order to construct and test an FPGA controller for quantum computing research, a team of Fermilab engineers lead by senior principle engineer Gustavo Cancelo collaborated with the University of Chicago to develop the faster and more cost-effective controllers. The University of Chicago’s lab, led by physicist David Schuster, assisted with the specifications and verification on real hardware. He is a member of the faculty.

“This is exactly the type of project that brings together the strengths of a national laboratory and a university,” said Schuster. Because of this, the quantum community has been quick to embrace an open-source control hardware environment.

Quantum computer engineers face the difficulty of bridging the gap between quantum and conventional computers. The principles of quantum physics, which control the tiny world, allow quantum computers to execute calculations that regular computers are unable to accomplish. Control and readout electronics serve as the translator between the macroscopic visible world and the world of classical physics, where people dwell.

The computer’s quantum bits, or qubits, are controlled by electronic signals from the classical world, while electronic readout measures the states of the qubits and transmits that information back to the classical world.

Superconducting circuits can serve as qubits in quantum computers, according to one promising technique. Most superconducting quantum computer control and readout systems now use commercial off-the-shelf technology that is not specialised for the task. Scientists are often forced to combine a dozen or more separate components because of this. Many of these devices are so massive that the cost per qubit can easily reach tens of thousands.

A qubit’s lifespan is only a few hundredths of a millisecond, and after that period, it begins to cause errors. “Time is of the essence when working with qubits. The computer’s performance is hampered since classical electronics takes longer to respond to qubits “opined Cancelo.

The turnaround time of a control and readout system is just as important as the ability of an interpreter to communicate effectively. Longer turn-around times are associated with complex systems comprised of numerous modules.

Fermilab’s Cancelo and his team came up with a compact control and readout system to meet this problem. They developed it. An electronics board the size of a laptop was used to house all the functions of a rack-mounted system. Despite its specificity, the novel method can be used with a wide range of superconducting qubit designs.

This instrument will cover qubits that will be developed in the next six to twelve months, according to Cancelo. If you’re looking to get the most out of your equipment, you’ll need our control and readout electronics.

Superconducting quantum computers’ present control and readout systems rely on off-the-shelf commercial technology that requires researchers to link together a dozen or more pricey components, resulting in an enormous and expensive control system. The University of Chicago is the source of this information.

For qubit control and readout, radio waves at frequency similar to those used in mobile phone calls and microwave dinners are used: microwave pulses. More than 200 components make up the Fermilab team’s radio frequency (RF) board, which includes mixers, filters, amplifiers, and attenuators, as well as switches to turn signals on and off. Additionally, the board includes a low-frequency control that can be used to fine-tune particular qubit settings. Researchers may successfully connect with the quantum realm using the RF board in conjunction with a commercial field-programmable gate array (FPGA) board.

A traditional system would cost 10 times as much to produce as the two small boards on this system. It is possible to control eight qubits in their simplest arrangement. Real-time error corrections and speedier operation can be achieved by integrating all of the RF components on one board.

One of the scientists involved in the experiment said that “you need to inject signals that are extremely fast and extremely short,” according to the Fermilab engineer. “Your qubit won’t act the way you want it to if you don’t regulate both the frequency and the duration of these signals very accurately.”

To ensure that signals could pass freely without bouncing or interfering, the RF board and layout had to be meticulously designed over the course of around six months. The engineers were also concerned about picking up stray radio waves from sources like cell phones and WiFi, so they had to be careful in their design. They used simulations to make sure they were on the proper path as they progressed.

Once fabrication and assembly have been completed, functioning RF boards are expected this summer.

The Fermilab engineers put their theories to the test with the University of Chicago throughout the procedure. The new RF board is excellent for researchers like Schuster, who are interested in making fundamental improvements in quantum computing employing a wide range of quantum computer architectures and components.

In his lab, “I often joke that this one board might potentially replace practically all of the test equipment that I have,” says Schuster. “Working with folks who are capable of making electronics operate at such a high level is a huge bonus for us.”

Scalability of the new system is not a problem at all. A single RF board may control up to 80 qubits using frequency multiplexing, which is akin to sending several phone calls over the same wire. One or more dozen boards could be connected to the same clock in a bigger quantum computer because of their modest size. In a piece just published in the AIP Review of Scientific Instruments, Cancelo and his colleagues detailed their novel approach.

New commercial FPGA chips, the first to incorporate digital-to-analog and analog-to-digital converters directly into the board, have been used by Fermilab engineers. It significantly speeds up the process of developing the interface between the FPGA and RF boards, which would have required months without it. FPGA hardware has been designed by the team in order to improve future generations of the control and readout system.

QuantISED, the Quantum Science Center (QSC), and eventually the Fermilab-hosted Superconducting Quantum Materials and Systems Center (SQMSC) funded the development of QICK (SQMS). Researchers at the SQMS are constructing superconducting qubits with long lifetimes using QICK circuits. In addition, the QSC at Oak Ridge National Laboratory, which hosts a second national quantum centre that includes Fermilab, is interested in it.

Only universities can now get a low-cost version of the hardware. According to Cancelo, it “allows smaller organisations to have robust quantum control without the need to spend hundreds of thousands of dollars.”

According to him, it’s an opportunity to work on one of the most hotly debated problems in physics of the last decade. “From an engineering perspective, what I like about this project is that it requires a wide range of electronic engineering disciplines to work together.”

Further information: Leandro Stefanazzi et al, The QICK (Quantum Instrumentation Control Kit): Readout and control for qubits and detectors, Review of Scientific Instruments (2022). DOI: 10.1063/5.0076249

Journal information: Review of Scientific Instruments

Source: Fermi National Accelerator Laboratory