Engineers develop new control electronics for quantum computers that improve performance and reduce costs

When designing a next-generation quantum computer, bridging the communication gap between the classical and quantum worlds is a surprisingly important issue. Such computers need specialized control and readout electronics to translate back and forth between the human operator and quantum computer languages ​​- but existing systems are cumbersome and expensive.

However, a new system of control and readout electronics, known as the Quantum Instrumentation Control Kit, or QICK, developed by engineers at the US Department of Energy’s Fermi National Accelerator Laboratory, has been shown to significantly improve the performance of quantum computers while reducing control equipment costs. .

“The development of the Quantum Instrumentation Control Kit is an excellent example of US investment in joint quantum technology research with industrial-university-government partnerships to accelerate quantum research and development technologies. Pre-competitive,” said Harriet Kung, DOE Deputy Director of Science. programs for the Office of Science and Acting Associate Director of Science for High Energy Physics.

The faster, more cost-effective controls were developed by a team of Fermilab engineers led by Senior Principal Engineer Gustavo Cancelo in collaboration with the University of Chicago, whose goal was to create and test an FPGA (field programmable gate array-based) controller for quantum computation experiments. David Schuster, a physicist at the University of Chicago, headed the university’s laboratory, which helped with specifications and verification of genuine hardware.

“It’s exactly the type of project that combines the strengths of a national laboratory and a university,” Schuster said. “There is a clear need for an ecosystem of open source control hardware, and it is rapidly being adopted by the quantum society.”

Engineers who design quantum computers take on the challenge of bridging the two seemingly incompatible worlds of quantum computers and classical computers. Quantum computers are based on the counterintuitive, probabilistic rules of quantum mechanics that govern the microscopic world, allowing them to perform calculations that ordinary computers cannot. Because humans live in the macroscopic visible world where classical physics prevails, control and readout electronics act as an interpreter connecting these two worlds.

The control electronics use signals from the classical world as instructions for the quantum bits or qubits of the computer, while the readout electronics measure the states of the qubits and pass this information on to the classical world.

A promising technology for quantum computers uses superconducting circuits as qubits. Currently, most control and readout systems for superconducting quantum computers use commercial equipment that is not specialized for the task. As a result, researchers often have to assemble a dozen or more expensive components. The cost can quickly reach tens of thousands of dollars per qubit, and the large size of these systems creates several problems.

Despite recent technological advances, qubits still have a relatively short lifespan, typically a fraction of a millisecond, after which they generate errors. “When working with qubits, time is of the essence. Conventional electronics take time to respond to qubits, which limits computer performance, ”Cancelo said.

Just as the efficiency of an interpreter depends on fast communication, the efficiency of a control and reading system depends on its execution time. And a large system consisting of many modules means long lead times.

To solve this problem, Cancelo and his team at Fermilab have designed a compact control and playback system. The team integrated the capabilities of an entire rack of equipment into a single printed circuit board that is slightly larger than a laptop. The new system is specialized but versatile enough to be compatible with many superconducting qubit designs.

“We are designing a general instrument for a wide range of qubits, hoping to cover those that will be designed in six months or a year,” Cancelo said. “With our control and readout electronics, you can achieve features and performance that are difficult or impossible to achieve with commercial equipment. »

Controlling and reading qubits depends on microwave pulses – radio waves at frequencies similar to the signals that transmit telephone calls and heat microwave dinners. The Fermilab Team Radio Frequency (RF) Card contains more than 200 elements: mixers for adjusting frequencies; filters to remove unwanted frequencies; amplifiers and attenuators for adjusting the amplitude of the signals; and switches on and off turn signals. The card also includes a low frequency control to set some qubit parameters. Combined with an FPGA or field-programmable gate array card that acts as the “brain” of the computer, the RF card provides everything scientists need to be able to communicate with the quantum world.

Both compact discs cost about 10 times less to produce than conventional systems. In their simplest configuration, they can control eight qubits. Integrating all RF components into a single card enables faster and more accurate operation as well as real-time feedback and error correction.

“You have to inject very, very fast and very, very short signals,” said Fermilab engineer Leandro Stefanazzi, a member of the team. “If you do not control the frequency and duration of these signals very precisely, your qubit will not behave the way you want it to.”

The design of the RF card and the layout took about six months and presented significant challenges: adjacent circuit elements had to be matched precisely so that signals could propagate smoothly and without interference with each other. In addition, engineers had to carefully avoid setups that would pick up stray radio waves from sources such as cell phones and WiFi. Along the way, they ran simulations to make sure they were on the right track.

The design is now ready for manufacture and assembly, with the goal of having functional RF boards for the summer.

Throughout the process, Fermilab engineers tested their ideas with the University of Chicago. The new RF card is ideal for researchers like Schuster who want to make fundamental advances in quantum computation using a wide range of quantum computational architectures and devices.

“I often joke that this board will potentially replace almost all the test equipment I have in my lab,” Schuster said. “It’s incredibly rewarding for us to team up with people who can make electronics work at this level.”

The new system is easily scalable. Frequency multiplexing qubit controllers, analogous to sending multiple telephone calls over the same cable, would allow a single RF card to control up to 80 qubits. Thanks to their small size, several dozen whiteboards could be linked together and synchronized on the same clock as part of larger quantum computers. Cancelo and his colleagues described their new system in an article recently published in AIP Study of scientific instruments.

Fermilab’s engineering team leveraged a new commercial FPGA chip, the first to integrate digital-to-analog and analog-to-digital converters directly into the card. It dramatically speeds up the process of creating the interface between FPGA and RF cards, which would have taken months without it. To improve future versions of their control and playback system, the team began designing its own FPGA hardware.

The development of QICK was supported by QuantISED, the Quantum Science Center (QSC) and later by the Superconducting Quantum Materials and Systems Center (SQMS), which hosts Fermilab. QICK electronics is important for research at SQMS, where researchers are developing long-lived superconducting qubits. It is also of interest to another National Quantum Center, where Fermilab plays a key role, QSC, which hosts the Oak Ridge National Laboratory.

A low-cost version of the hardware is now only available to universities for educational purposes. “Because of its low cost, it allows small institutions to have powerful quantum control without spending hundreds of thousands of dollars,” Cancelo said.

“From a scientific point of view, we are working on one of the hottest physics topics of the decade as an option,” he added. “From a technical point of view, I appreciate that many areas of electronics need to be brought together in order to complete this project. »

Fermi National Accelerator Laboratory is the United States’ leading national laboratory for particle physics and accelerator research. A laboratory from the U.S. Department of Energy’s Office of Science, Fermilab, is located near Chicago, Illinois, and is operated under contract by Fermi Research Alliance LLC, a partnership between the University of Chicago and the Universities Research Association, Inc. Visit?Fermilab website? and follow us on Twitter at?@Fermilab.

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