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Faster method to read quantum memor

Artistic impression of qubit (blue chip) readout using the quantum states of a resonator (blue and red jets). Figure credit: Heikka Valja.

Faster method to read quantum memory

Tommi Kutilainen

Scientists at Aalto University and VTT have developed a faster way to read information out of qubits, the basic building blocks of a quantum computer.

The potential computing revolution that quantum computers promise is based on their weird property called superposition. Namely, qubits can take both logical states 0 and 1 simultaneously, and any value in between. By mastering superpositions of the whole quantum memory, quantum computers can quickly solve problems that would require too much computing time from regular computers working with simply 0s and 1s.

However, qubits are sensitive, and currently hold quantum information for less than a millisecond at a time, even when kept frozen at temperatures colder than the dark side of the moon. To extract any useful information, the method that reads information from qubits must take the least amount of time as possible, allowing as few errors as possible.

Joni Ikonen, a PhD student at Aalto University, has developed a new method published in Physical Review Letters that helps do just that. Until now, the method used to read information from a qubit was to apply a short microwave pulse to the superconducting circuit containing the qubit and then measure the reflected microwave. After 300 nanoseconds, the state of the qubit can be deduced from the behavior of the reflected signal.

Jan Goetz (left), Joni Ikonen (middle), and Mikko Möttönen (right). Figure credit: Aalto University.

– We were able to complete the readout in 300 nanoseconds in our first experiments, but we think that going below 100 nanoseconds is just around the corner, says Joni Ikonen.

By improving the speed and accuracy of the information retrieved from qubits, scientists may be able to move closer to realising the promise of useful quantum computing.

– This is an amazing result in getting the slippery qubits in order. I hope that it will help the community in the future to reach quantum supremacy and error correction, the path to a quantum computer of practical value, says Dr. Möttönen, who co-supervised the work with Dr. Jan Goetz

The QCD research team is part of the national centre of excellence – Quantum Technology Finland, funded by the Academy of Finland. The experimental research was carried out at the national OtaNano research infrastructure for micro, nano, and quatum technologies.

Quantum chip mounted on a sample holder. Figure credit: Aalto University.

More information:

Joni Ikonen, Jan Goetz, Jesper Ilves, Aarne Keränen, Andras M. Gunyho, Matti Partanen, Kuan Y. Tan, Leif Grönberg, Visa Vesterinen, Slawomir Simbierowicz, Juha Hassel, and Mikko Möttönen, Qubit Measurement by Multi-Channel Driving, Physical Review Letters 122, 080503 (2019). https://doi.org/10.1103/PhysRevLett.122.080503 (preprint arXiv)

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