A new approach to controlling qubits with microwave pulses reduces error rates and improves efficiency

The inside of the apparatus in which the ions are located. A close-up shows an image of two separate 9Be + ions used for quantum gates. Courtesy: T. Dubielzig, H. Khan (LUH / PTB).

A functional quantum computer is one of the most intriguing promises of quantum technology. With significantly increased processing power, quantum computers will be able to solve tasks that conventional computers cannot perform, such as understanding and inventing new materials or pharmaceuticals, as well as testing the limits of cryptographic methods.

As in conventional computers, the term quantum bit or qubit refers to the basic unit in quantum information. Currently, the most advanced approaches for their implementation are superconducting chains and trapped ions. Former Stores quantum information in electronic components, the latter at different energy levels of individual atoms. Using superconducting circuits, researchers have recently been able to demonstrate that quantum computers are capable of performing highly specialized tasks that ordinary computers cannot perform. However, unlike any other approach, ions produce significantly less error rates in transactions.

To further reduce errors and ensure reliable operation, researchers at the Leibniz University in Hanover and the Physikalisch-Technische Bundesanstalt (PTB) have now developed a new method. Their findings were published in the latest issue of the scientific journal. Physical Review Letters,

When they approach, ions are captured in vacuum using electric fields above the chip structure. Qubit operations are done by sending microwave signals through special conductor loops embedded in the chip structure. Logical operations are usually performed using extremely carefully controlled laser beams. The advantage of using microwave fields is that they are relatively easy to operate and are highly developed technology because they are ubiquitous in numerous products, from airplanes to mobile phones.

As part of the study, the researchers investigated the most effective methods of operations on qubits. This is also a very urgent problem in ordinary a computer microcircuits, since the amount of energy required for each operation determines how many of them can be processed per second before the microcircuit starts to overheat. As for microwave quantum computers with an ion trap, the researchers were able to demonstrate that microwave pulses of a certain shape, when the field smoothly turns on and off, give 100 times fewer errors than those in which the fields simply turn on and off – with the same Energy Supply and despite the presence of noise. To this end, the team introduced an additional and carefully controlled noise into the experiment and identified operational errors for various levels of introduced noise, as well as for both pulse shapes. “It was of great importance for our experiment,” said Giorgio Zarantonello, one of the authors of the study. “In the past, searching for suitable operations included a lot of trial and error, as well as a long optimization process, before seizing the moment with very little noise. All we need to do now is turn on the experiment, and it works. ”

After demonstrating that basic low-error operations are possible, researchers are now striving to transfer their findings to more complex tasks. The intention is to achieve less than one error for every ten thousand operations, that is, when scaling to a large number of qubits becomes effective. To this end, they have already developed a patented microprocessing technology that supports the storage and handling of a large number of qubits in chip structures.

Improving quantum computers

Additional Information:
G. Zarantonello et al. Reliable and resource-saving near field satellite Be + 9 Gate, Physical Review Letters (2019). DOI: 10.1103 / PhysRevLett.123.260503

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University of Leibniz, Hanover

A new approach to controlling qubits using microwave pulses reduces the frequency of errors and increases efficiency (January 10, 2020)
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