In recent years, the development of quantum computing has boomed, and many important technological milestones have been taken. However, a problem remains: the number of usable qubits (quantum bits) remains strongly constrained by the electronic control systems employed; the latter being generally bulky and producing a heat which is difficult to reconcile with the quantum environment of the qubits. However, a team of researchers may have solved part of the problem by developing a cryogenic chip capable of providing electronic management of qubits at temperatures close to absolute zero. This would significantly increase the number of usable qubits, and therefore the power of future quantum computers.
Researchers have developed a new type of cryogenic computer chip capable of operating at temperatures so cold that it approaches the theoretical limit of absolute zero. This cryogenic system, called the Gooseberry, lays the groundwork for what could be a revolution in quantum computing - allowing a new generation of machines to perform calculations with thousands of qubits or more, while the most advanced devices today only include dozens.
“ The largest quantum computers in the world currently operate with only 50 qubits. This small scale is in part due to the limits of the physical architecture that controls qubits, ”explains quantum physicist David Reilly of the University of Sydney and Microsoft's quantum laboratory.
A quantum environment requiring extreme temperatures
This physical architecture is constrained due to the extreme conditions that qubits need to perform quantum calculations. Unlike binary bits in traditional computers, which take a value of 0 or 1, qubits are based on quantum superposition, allowing values of 0, 1 and both simultaneously.
A qubit can take the values 0, 1 and 0/1 (superposition). To maintain the principle of quantum superposition, qubits must be placed in an extremely cold environment, thus limiting their number. © IBM
This principle of quantum mechanics means that quantum computers can theoretically solve extremely complex mathematical problems that classical computers could never answer (or take years to do). To date, researchers have been limited in the number of qubits they have been able to successfully deploy in quantum systems.
One reason for this is that qubits require extreme levels of cold to function (in addition to other controlled conditions), and the electrical wiring used in today's quantum computing systems inevitably produces levels of low but sufficient heat which disrupts thermal requirements. Scientists are looking for ways to get around this, but many quantum innovations to date depend on designing large cabling platforms to keep temperatures stable to increase the number of qubits, but this solution has its own limitations.
The solution to this bottleneck could be Gooseberry: a cryogenic control chip that can operate at “millikelvin” temperatures, just a tiny fraction of a degree above absolute zero. This extreme heat capacity means the chip can fit inside the super cold refrigerated environment of the qubits, interface with them, and pass the signals from the qubits to a secondary core that sits outside in a another extremely cold tank, submerged in liquid helium.
Image of the Gooseberry cryogenic chip (red) next to the test chip containing the qubits (blue) and an electronic resonator (purple). © Microsoft
In doing so, it removes all the excess wiring and the excess heat they generate, meaning that qubit bottlenecks in quantum computing may soon be a thing of the past. “ This chip is the most complex electronic system capable of operating at this temperature. This is the first time that a mixed signal chip with 100,000 transistors has operated at -273.05 ° C, ”explains Reilly.
Ultimately, the team expects their system to be able to allow thousands of qubits to be controlled by the cryogenic chip - about 20 times more than is possible today. In the future, the same kind of approach could allow quantum computers to operate on a whole new level.