Newly designed microwave source could replace existing bulky control systems that hamper quantum computer scalability – sciencedaily

Finnish researchers have developed a circuit that produces the high-quality microwave signals needed to control quantum computers while operating at temperatures near absolute zero. This is a key step in bringing the control system closer to the quantum processor, which can significantly increase the number of qubits in the processor.

One of the factors limiting the size of quantum computers is the mechanism used to control qubits in quantum processors. This is normally accomplished using a series of microwave pulses, and since quantum processors operate at temperatures near absolute zero, control pulses are normally brought into the cooled environment via wide cables. strip from room temperature.

As the number of qubits increases, so does the number of cables required. This limits the potential size of a quantum processor, as fridges cooling qubits would have to grow larger to accommodate more and more cables while working harder to cool them – ultimately a losing proposition.

A research consortium led by Aalto University and the VTT Technical Research Center of Finland has now developed a key part of the solution to this conundrum. “We have built a precise microwave source that operates at the same extremely low temperature as quantum processors, around -273 degrees,” says Mikko Möttönen, professor at Aalto University and VTT Technical Research Center of Finland, who led the team.

The new microwave source is a device-on-a-chip that can be integrated with a quantum processor. Being less than a millimeter in size, it potentially eliminates the need for high frequency control cables connecting different temperatures. With this low power, low temperature microwave source, it may be possible to use smaller cryostats while increasing the number of qubits in a processor.

“Our device produces a hundred times more power than previous versions, which is enough to control qubits and perform quantum logic operations,” explains Möttönen. “It produces a very precise sine wave, oscillating over a billion times per second. As a result, errors in the qubits of the microwave source are very rare, which is important when performing precise quantum logic operations. ‘

However, a continuous wave microwave source, such as that produced by this device, cannot be used as is to control qubits. First, microwaves must be shaped into pulses. The team is currently developing methods to quickly turn the microwave source on and off.

Even without a switching solution to create pulses, an efficient, low noise, low temperature microwave source could be useful in a range of quantum technologies, such as quantum sensors.

“In addition to computers and quantum sensors, the microwave source can act as a clock for other electronic devices. It can keep different devices at the same rate, allowing them to induce operations for several different qubits at the desired time, ”explains Möttönen.

The theoretical analysis and initial design was done by Juha Hassel and others at VTT. Hassel, who started this job at VTT, is currently responsible for engineering and development at IQM, a Finnish quantum computing hardware company. The device was then built at VTT and operated by postdoctoral researcher Chengyu Yan and colleagues at Aalto University using the OtaNano research infrastructure. Yan is currently an Associate Professor at Huazhong University of Science and Technology, China. The teams involved in this research are part of the Academy of Finland’s Center of Excellence in Quantum Technology (QTF) and the Finnish Quantum Institute (InstituteQ).

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Materials provided by Aalto University. Note: Content can be changed for style and length.


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