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A research team at the Tokyo Medical and Dental University (TMDU), RIKEN, and the University of Tokyo have demonstrated how to increase the lifetime of qubits inside quantum computers by using an additional "filter" qubit. This work may help make higher fidelity quantum computers that can be used in financial, cryptographic, and chemistry applications.
[...] there is a fundamental tradeoff between the lifetime of the qubit superpositions and the processing speed. This is because the qubits must be carefully shielded from interacting with the environment, or the fragile superposition will snap back to being just a one or zero in a process called decoherence. To delay this loss of quantum fidelity, qubits in quantum computers are coupled only weakly to the control line through which the qubit control pulses are applied. Unfortunately, such a weak coupling limits the speed that computations can be run.
Now, the team at the Tokyo Medical and Dental University (TMDU) theoretically show how coupling a second "filter" qubit to the control line can greatly reduce the noise and spontaneous radiative losses that lead to decoherence. This allows the connections to be strong, which lends itself to faster cycle times.
"In our solution, the filter qubit acts like a nonlinear mirror, which completely reflects radiation from the qubit due to destructive interference but transmits strong control pulses due to absorption saturation," says first author Kazuki Koshino.
This research helps bring about a future in which quantum computers can be found in every business and research lab. Many operational research firms would like to use quantum computers to solve optimization problems that were considered too intensive for conventional computers, while chemists would like to use them to simulate the motion of atoms inside molecules.
(Score: 0) by Anonymous Coward on Monday March 09 2020, @03:56AM (1 child)
slow clap
(Score: 2) by maxwell demon on Monday March 09 2020, @11:29AM
Wrong. Quantum error correction (parity bits are just the simplest form for error correction) is already a well-known subject and has been studied fro quite some time. In particular, error correction is, as the name says, aboutcorrecting errors after they happened.
This is not quantum error correction, and has nothing to do with parity bits. This is shielding of the qubit from the control line, in a way that the actual control pulses are not affected too much.
As a rough analogy, think of a computer with data that must be protected from unauthorized modification. Now because that data is valuable, security measures are high, but that also means that those who have to work with the data are massively slowed down. However if the security measures are lowered to allow working more efficiently with the data, hackers will get in and alter the data.
Now the solution they found to this problem is roughly as follows: They put a firewall (the second qubit) in front that filters all the data, but has a capacity limit. Now the hackers can only attack through an outside channel with limited capacity, which is well within the limits of the firewall. However those who are authorized to alter the data have sufficient capacity to saturate the firewall, therefore they can get their commands past it.
Note that this is only a very rough analogy (and certainly as security measure for computer systems, that would not be a good idea at all), but it is at least much closer than the parity bit.
The Tao of math: The numbers you can count are not the real numbers.