“Hot Qubits” are Here—And They’re Propelling the Future of Quantum Computing

April 25, 2020 by Robin Mitchell

Within a month, researchers around the world have released landmark studies on qubits operating above absolute zero temperatures. Does this mean commercial quantum computing is on the horizon?

Within the past month, researchers around the world are making landmark discoveries about quantum bits, or qubits. The biggest environmental factor that stands in the way of quantum computers entering commercial spaces is that qubits have a low tolerance to temperature; previously, they could only operate at temperatures close to absolute zero.

This is because a qubit storing a quantum state will collapse if "observed," or is affected by external factors. For example, a photon hitting a qubit will cause it to collapse and will offset a thermal vibration from a nearby particle.

This is why many scientists are working on creating quantum systems that can operate above these low temperatures. Such an effort will get them out of the laboratory and into the commercial field. In this article, we will look at recent scientific research that proves that "hot qubits," even up to room temperature, are now a reality.


Sydney Researchers' Groundbreaking "Hot Qubits"

A team of researchers from UNSW Sydney has worked to solve the problem of absolute-zero qubit requirements and may have a solution that works on regular silicon. The test device is a proof-of-concept quantum processor unit cell that can operate at temperatures up to 1.5 kelvin. While this may still sound extremely cold, it is still 15 times greater than those produced by others, including Google and IBM. The results of this research were published in Nature.


Researchers from UNSW Sydney stand beside a dilution refrigerator

Researchers from UNSW Sydney stand beside a dilution refrigerator, which keeps qubits operating at extremely cold temperatures. Image used courtesy of UNSW Sydney

The researchers created quantum chips that can operate in tandem with conventional silicon chips. When these two chips are set beside each other in low temperatures, they can control the read and write operations of quantum calculations.


Quantum chip placed in cool temperatures beside conventional silicon chip

Quantum chip placed in cool temperatures beside conventional silicon chip. Image used courtesy of UNSW Sydney

To prove the viability of the design, another team on the other side of the globe in the Netherlands used the same technology to create a hot qubit, which also functioned as expected. The design utilizes two qubits that are confined in a pair of quantum dots—all of which are embedded in silicon.

What also makes this research groundbreaking is that other laboratories can replicate this temperature feat with a few thousand dollars of equipment. This means that even small companies can access their own quantum computer. 

The fact that this technology can be built using silicon technology means that it can readily be integrated into existing electronic designs, feeding data into such systems and interpreting the results. 


Intel and QuTech Make Concurrent Discoveries With UNSW on Hot Qubits

On the same day that the Sydney researchers published their findings on "hot qubits," Intel also published its own research on hot qubits. Intel, one of the world's leading suppliers of processor and memory technology, teamed up with QuTech to produce a "hot qubit" that can operate at temperatures up to 1.1 kelvin. While not as high as the UNSW, the 1.1-kelvin mark is still an achievable temperature using low-cost equipment (when compared to absolute zero). The researchers for the project also published their findings in Nature.

The qubit designed by the team has a fidelity of 99.3%—that is, a high-quality qubit with a large degree of quantum separation between states. However, the performance of the spin qubits is minimally affected when temperatures go to 1.25 kelvin.


An isotopically pure wafer

An isotopically pure wafer Intel used to create spin qubit fabrication flow on its 300 mm process technology. Image used courtesy of Walden Kirsch/Intel Corporation 

The design, which works with standard silicon technology, demonstrates single-qubit control via the use of electron spin resonance and readout using the Pauli spin blockage method. The demonstrated device also shows individual coherent control of two qubits and turnability from 0.5 MHz to 18 MHz.

Because it can be integrated onto standard silicon technology, the qubit developed by Intel and QuTech can incorporate control circuitry and quantum processors onto a single device. 


Russian Researchers Redefine the "Hot Qubit" With Room-Temperature Qubits

While the Sydney and Intel teams have created qubits that operate at temperatures higher than absolute zero, a team from Russia together with colleagues from Sweden, Hungary, and the USA, have developed a method for manufacturing room-temperature qubits.

According to the research paper in Nature Communications, qubits have been proven to operate at room temperatures when integrated into point defects in diamonds, achieved by substituting a carbon atom with a nitrogen atom. However, producing such diamonds can be an expensive manufacturing task. This is where the Russian lead team has stepped up.


stabilize point-defect spin qubits by quantum wells

The researchers found that they could stabilize point-defect spin qubits by quantum wells. Image used courtesy of MISIS

The team determined that silicon carbide was a suitable substitute for diamond when a laser was used to hit a defect in the crystal. When bombarded with photons, the defect luminescences and the resultant spectroscopy show six distinctive peaks (PL1 to PL6).

It is these peaks that show SiC's ability to be used as a qubit and therefore what structure is needed. Thus, their method for creating room-temperature qubits would use a chemical vapor deposition of SiC—a low-cost alternative to diamond.

The discovery of SiC's use in quantum qubits has already lead to SiC-based high-accuracy magnetometers, biosensors, and quantum internet technologies.


The Future of Hot Qubits

A hot qubit that can operate on a piece of silicon alongside existing components would revolutionize the computing industry. 

While mainstream quantum computers are still a decade or two away, these advancements in qubit technology show how quantum technology will not be stuck in laboratories indefinitely and will eventually be open to the public. How will quantum technologies affect electronic engineers remains unknown since we do not know how far quantum integration will go.

Will they be integrated into microcontrollers? Will devices need to deploy quantum security? Only time will tell.