Engineers develop new control electronics for quantum computers that
improve performance, cut costs

Date:
April 29, 2022
Source:
DOE/Fermi National Accelerator Laboratory
Summary:
Quantum computing experiments now have a new control and readout
electronics option that will significantly improve performance
while replacing cumbersome and expensive systems.



FULL STORY ==========================================================================
When designing a next-generation quantum computer, a surprisingly large
problem is bridging the communication gap between the classical and
quantum worlds.

Such computers need a specialized control and readout electronics to
translate back and forth between the human operator and the quantum
computer's languages -- but existing systems are cumbersome and expensive.


========================================================================== However, a new system of control and readout electronics, known as Quantum Instrumentation Control Kit, or QICK, developed by engineers at the U.S.

Department of Energy's Fermi National Accelerator Laboratory, has proved
to drastically improve quantum computer performance while cutting the
cost of control equipment.

"The development of the Quantum Instrumentation Control Kit is an
excellent example of U.S. 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 programs for the Office of Science and acting associate director of science for high-energy physics.

The faster and more cost-efficient 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 a field-programmable gate array-based (FPGA) controller for quantum computing experiments. David Schuster, a physicist at the University of Chicago, led the university's lab that helped with the specifications
and verification on real hardware.

"This is exactly the type of project that combines the strengths of
a national laboratory and a university," said Schuster. "There is a
clear need for an open-source control hardware ecosystem, and it is
being rapidly adopted by the quantum community." Engineers designing
quantum computers deal with the challenge of bridging the two seemingly incompatible worlds of quantum and classical computers. Quantum
computers are based on the counterintuitive, probabilistic rules of
quantum mechanics that govern the microscopic world, which enables them
to perform calculations that ordinary computers cannot. Because people
live in the macroscopic visible world where classical physics reigns,
control and readout electronics act as the interpreter connecting these
two worlds.



========================================================================== Control electronics use signals from the classical world as instructions
for the computer's quantum bits, or qubits, while readout electronics
measure the states of the qubits and convey that information back to
the classical world.

One promising technology for quantum computers uses superconducting
circuits as qubits. Currently, most control and readout systems for superconducting quantum computers use off-the-shelf commercial equipment
not specialized to the task.

As a result, researchers often must string together a dozen or more
expensive components. The cost can quickly add up to tens of thousands
of dollars per qubit, and the large size of these systems creates more problems.

Despite recent technological advances, qubits still have a relatively
short lifetime, generally a fraction of a millisecond, after which they generate errors. "When you work with qubits, time is critical.Classical electronics take time to respond to the qubits, limiting the performance
of the computer," said Cancelo.

Just as the effectiveness of an interpreter depends on rapid
communication, the effectiveness of a control and readout system depends
on its turnaround time.

And a large system made of many modules means long turnaround times.

To address this issue, Cancelo and his team at Fermilab designed a compact control and readout system. The team incorporated the capabilities of an
entire rack of equipment in a single electronics board slightly larger
than a laptop.

The new system is specialized, yet it is versatile enough to be compatible
with many designs of superconducting qubits.



==========================================================================
"We are designing a general instrument for a large variety of qubits,
hoping to cover those that will be designed six months or a year from
now," Cancelo said.

"With our control and readout electronics, you can achieve functionality
and performance that is hard or impossible to do with commercial
equipment." The control and readout of qubits depend on microwave pulses
-- radio waves at frequencies similar to the signals that carry mobile
phone calls and heat up microwave dinners. The Fermilab team's radio
frequency (RF) board contains more than 200 elements: mixers to tweak
the frequencies; filters to remove undesired frequencies; amplifiers
and attenuators to adjust the amplitude of the signals; and switches
to turn signals on and off. The board also contains a low- frequency
control to tune certain qubit parameters. Together with a commercial field-programmable gate array, or FPGA, board, which serves as the
"brains" of the computer, the RF board provides everything scientists
need to communicate successfully with the quantum world.

The two compact boards cost about 10 times less to produce than
conventional systems. In their simplest configuration, they can control
eight qubits.

Integrating all the RF components into one board allows for faster,
more precise operation as well as real-time feedback and error correction.

"You need to inject signals that are very, very fast and very, very
short," said Fermilab engineer Leandro Stefanazzi, a member of the
team. "If you don't control both the frequency and duration of these
signals very precisely, then your qubit won't behave the way you want." Designing the RF board and layout took about six months and presented substantial challenges: adjacent circuit elements had to match precisely
so that signals would travel smoothly without bouncing and interfering
with each other. Plus, the engineers had to carefully avoid layouts
that would pick up stray radio waves from sources like cell phones and
WiFi. Along the way, they ran simulations to verify that they were on
the right track.

The design is now ready for fabrication and assembly, with the goal of
having working RF boards this summer.

Throughout the process, the Fermilab engineers tested their ideas with
the University of Chicago. The new RF board is ideal for researchers
like Schuster who seek to make fundamental advances in quantum computing
using a wide variety of quantum computer architectures and devices.

"I often joke that this one board is going to potentially replace
almost all of the test equipment that I have in my lab," said
Schuster. "Getting to team up with people who can make electronics
work at that level is incredibly rewarding for us." The new system is
easily scalable. Frequency multiplexing qubit controls, analogous to
sending multiple phone conversations over the same cable, would allow
a single RF board to control up to 80 qubits. Thanks to their small
size, several dozen boards could be linked together and synchronized
to the same clock as part of larger quantum computers. Cancelo and his colleagues described their new system in a paper recently published in
the AIPReview of Scientific Instruments.

The Fermilab engineering team has taken advantage of a new commercial
FPGA chip, the first to integrate digital-to-analog and analog-to-digital converters directly into the board. It substantially speeds up the process
of creating the interface between the FPGA and RF boards, which would
have taken months without it. To improve future versions of its control
and readout system, the team has started designing its own FPGA hardware.

The development of QICK was supported by QuantISED, the Quantum Science
Center (QSC) and later by the Fermilab-hosted Superconducting Quantum
Materials and Systems Center (SQMS). The QICK electronics is important
for research at the SQMS, where scientists are developing superconducting qubits with long lifetimes. It is also of interest to a second national
quantum center where Fermilab plays a key role, the QSC hosted by Oak
Ridge National Laboratory.

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

"From a scientific point of view, we are working on one of the hottest
topics in physics of the decade as an opportunity," he added. "From an engineering point of view, what I enjoy is that many areas of electronic engineering need to come together to be able to successfully execute this project." Fermi National Accelerator Laboratory is America's premier
national laboratory for particle physics and accelerator research. A
U.S. Department of Energy Office of Science laboratory, Fermilab is
located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC, a joint partnership between the University of
Chicago and the Universities Research Association, Inc. Visit?Fermilab's website?and follow us on Twitter at?@Fermilab.


========================================================================== Story Source: Materials provided by
DOE/Fermi_National_Accelerator_Laboratory. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Leandro Stefanazzi, Kenneth Treptow, Neal Wilcer, Chris Stoughton,
Collin
Bradford, Sho Uemura, Silvia Zorzetti, Salvatore Montella,
Gustavo Cancelo, Sara Sussman, Andrew Houck, Shefali Saxena,
Horacio Arnaldi, Ankur Agrawal, Helin Zhang, Chunyang Ding,
David I. Schuster. The QICK (Quantum Instrumentation Control Kit):
Readout and control for qubits and detectors. Review of Scientific
Instruments, 2022; 93 (4): 044709 DOI: 10.1063/5.0076249 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220429144931.htm

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