What Will Quantum Computer Components Look Like?

Created: March 29, 2022
Updated: October 10, 2024

I remember being in college over a decade ago and hearing about quantum computers in my upper-level physics classes. At the time, it was hard enough for me to understand the core concepts and for the professor to explain them. Fast forward to today, and quantum computers have finally become a reality, and the mission has become one of scaling the technology. If you’re a quantum algorithm developer, you can even rent time on a quantum computer via the cloud and run your own quantum applications.

Not many people have seen the inside of a quantum computer until probably the last two years when many tech giants started publicizing some details of their systems. Now that we’ve had the privilege of seeing some of the finer details that go into building quantum systems, it becomes easier to see what some of the main components of a quantum computer look like, as well as what functions they perform. Aside from the structures used in qubit processors, quantum computer components have plenty of resemblance to their classical counterparts.

At the moment, the most important portion of a quantum computer (the qubit processor) is entirely custom, but there are a host of other subsystems that make a quantum computer operate. PCB designers may play a larger role than they think in helping to commercialize these systems. Without getting too deep into what is a quantum computer, I’ll do my best to explain the roles played by different quantum computer components.

What Makes a Computer “Quantum?”

All quantum computers use quantum bits, or qubits, to process information. The popular explanation for a quantum computer is that it leverages the fact that a qubit can exist as a superposition (or combination) of information states, which is interpreted as the qubits in a quantum computer’s processor being in some mix of 0 and 1 states simultaneously. The alternative philosophical view of quantum mechanics (or the “Many Worlds” interpretation) holds that quantum computers are inherently parallelized machines, with copies of a quantum computer running multiple computations in parallel universes!

Whatever physical picture helps you best understand the behavior of qubits, the qubits themselves are only half the story. The other half relies on the use of entanglement, a phenomenon that still baffles physicists. Einstein described it as “spooky action at a distance” as it allows qubits to be written into the same quantum state, even when separated by extremely long distances. This brings up things like faster-than-light communication and has even spawned applications like quantum radar.

What a Quantum Computer Does

A quantum computer is designed to manipulate and read out qubits, which may be entangled with other qubits, or which may be in some superposition of 0’s and 1’s. This relies on a number of important components and subsystems. Although a quantum computer uses qubits, the supporting subsystems that make it work as designed are all classical components, right down to the passives used in circuit boards.

Here’s what’s needed to ensure a quantum computer operates as designed:

Isolation from the Environment vs. Integration

The quantum processor, and the qubits it contains, must be heavily isolated from the environment. When a qubit interacts with the surrounding environment (through absorbing light or heat), the current state of a qubit can be lost, creating an error. Ensuring isolation involves the use of high vacuum systems and refrigeration to prevent a qubit from experiencing decoherence.

This is where a number of components and systems are needed to ensure isolation:

  • Ultra-high vacuum pumps

  • Dilution refrigeration systems

  • Low-temperature thermostat systems

  • Electromagnetic shielding

  • Tubing for liquid helium and liquid nitrogen refrigerant

Controlling these systems requires a classical processor to read out vacuum and temperature measurements and make adjustments to vacuum power and temperature. This doesn’t require massive classical computing power. A typical MPU or FPGA contains enough processing power to run these control systems and ensure isolation, as well as to deliver data to an application running on a classical computer. Continue to zoom out, and there may be networking equipment and other systems around the main column in a quantum computer that allows it to interface with other systems via the cloud. The isolation requirement has been a double-edged sword for all of this until just recently.

At the end of February 2022, it was announced that Researchers at the US National Institute of Standards and Technology (NIST) constructed and tested a system that allows commercial components on standard circuit boards to operate in close proximity with ultra-cold devices used in quantum computers. The challenge with integration at the circuit board level is the heat generated by conventional electronics can cause a qubit to experience decoherence, which destroys the quantum state and creates an error. This is just one step towards integrating quantum and classical components at the system level.

Another recent advance involves integration at the chip level. In early February, researchers at École Polytechnique Fédérale de Lausanne (EPFL) and the Hitachi Cambridge Laboratory designed a 40 nm CMOS integrated circuit with silicon quantum dots and conventional time-domain multiplexed readout circuits on the same die. While not a general purpose processor, the result illustrates the possibility of building quantum computing components at scale with a standard CMOS process.

Quantum Processors

The main component that makes a quantum computer run is the quantum processor. There are different flavors of quantum processors (photonic, spintronic, ion trap, and others), just like classical processors. Most recently, ion trap quantum processors have been shown to provide greater isolation for qubits. In addition, they provide greater computing power with a lower qubit count compared to other processors.

As of March 28, 2022, you can now purchase a 25-qubit quantum processing unit (QPU) from QuantWare, a company spun out of Delft University in the Netherlands. Previously, the company released a 5-qubit off-the-shelf processor in July 2021. QuantWare wants to become one of the premier chip manufacturers that develop and produce small-scale quantum processors. Currently, their custom 25 qubit quantum processors can be delivered to customers in 30 days. It logically follows that quantum ASICs and quantum SoCs are next on the list of available products.

While QuantWare’s new product offering is not the only quantum processor to have ever been created, it is certainly the first to be made commercially available as an off-the-shelf component. Some of the notable quantum processors from recent memory include systems announced by the likes of Intel, IBM, Honeywell, the University of Science and Technology of China, and Rigetti. The hardware ecosystem to support quantum computing is starting to grow quickly, but it requires a lot more than quantum processors.

Superconducting Circuits

Input and output data from a quantum processor must be fed back to a readout system using circuits made from superconducting materials. These interface and readout circuits must be brought down to temperatures of ~10 mK. Just for comparison, the background temperature of the universe is only ~3 K. Ultimately, these circuits connect back to a readout system (see below) so that data can be captured.

Superconducting materials (aside from copper oxides at less than ~35 K) are not something that can be sourced commercially. The superconducting circuitry used in quantum processors and readout interconnects is currently custom-made, but these eventually interface with a set of microwave components. This is where RF designers and the components they use become critical.

Coherent Microwave Sources/Detectors and Coax Cables

Even quantum computers have fallen victim to shortages of specialized components. In a recent MIT Technology Review article, Martin Giles lamented “We’d have more quantum computers if it weren’t so hard to find the damn cables.” Although some specialized superconducting cables are needed to transfer data, they connect back to a set of classical components for reading out data.

Standard components used in RF front-ends can be used at the top of the column to source, amplify, and capture readout signals, which are then converted into classical bits with high bandwidth/low noise ADCs. This is a bit simplistic as there is a series of amplifiers, filters, and a detector used to condition and capture the readout signal. While the perception of quantum as a super-advanced set of technologies creates the impression that advanced RF components are needed, these systems are operating at moderate mmWave frequencies. For example one of Intel’s readout systems is operating at only 20 GHz, which is comfortably within the operating range of many RF systems.

Challenges and Opportunities

Standardization

Currently, all the classical electronics used in control systems for quantum computers are custom-made from discrete components. Integration of these systems will aid miniaturization, just as has occurred in classical computers over time. The responsibility for this is split between chipmakers, electronics designers, and quantum systems integrators. Chipmakers are unlikely to step up to the plate anytime soon, putting the onus on systems designers to integrate control and readout systems.

To commercialize these technologies and bring new products to market, they must be interoperable with conventional electronics and each other, something which is being actively pursued. Making quantum computers interoperable, more powerful (this is about more than just qubit count), and miniaturized also requires taking a modular approach, something which will be enabled by greater standardization. Organizations like the Quantum Economic Development Consortium (full disclosure: I am a former member of their workforce development committee) are focusing on developing these standards to aid greater commercialization.

Greater standardization of components will help more designers get involved in developing new systems to support quantum computing. As more quantum components and systems become standardized and commercialized, they’ll be more seamlessly integrated with larger electronic systems. Currently, classical computers are used for control and readout systems, as well as to connect quantum computers to the cloud.

Real Market Growth

As for market growth over the next few years, projections of market size range from $830 million to $5 billion by 2024, and we’re well on our way to reaching that goal. Wall Street has started to take notice, and some well-known quantum computing names were taken public through billion-dollar SPAC mergers in 2021. Whether this technology is overhyped or will deliver the next wave of massive technological innovation remains to be seen, but designers will likely see some of the first commercially available quantum systems and development tools become available very soon.

As quantum computer components and systems become commercialized, Octopart will be here to give supply chain management features to designers. No matter what type of system or subsystem you’re designing to support quantum computers, Octopart’s search engine includes advanced filtration features to help you select exactly the components you need. Take a look at our integrated circuits page to start the search for your ideal components.

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