![]() ![]() In addition, the passive method can partially suppress noise, so that there are fewer errors in the first place. The new method can correct photon loss errors at rates up to 10 times faster than those achieved by active, measurement-based methods. The combination of careful tuning of the resonant frequencies of the circuit and adding photons two at a time to correct losses ensures that the passive error correction circuit can operate continuously but won't do anything to the two good qubits unless their oscillation has been broken by a photon loss." When a photon randomly escapes from the circuit, the oscillation is broken, at which point a second, passive error correction circuit kicks in and quickly inserts two photons, one which restores the lost photon and reconstructs the oscillating logical state, and the other is dumped to a lossy circuit element and quickly leaks back out of the system. "However, like all qubits, the qubits in the circuit are not perfect and will slowly leak photons into the environment. "In the absence of any errors, there are a pair of oscillating photon configurations that are the 'good' logical states of the device, and they oscillate at a fixed frequency based on the circuit parameters," Kapit explained. The two qubits are coupled to each other, and each one is also coupled to a "lossy" object, such as a resonator, that experiences photon loss. ![]() The new passive error correction circuit consists of just two primary qubits, in contrast to the 10 or more qubits required in most active approaches. While this paper is a theoretical blueprint, it can be built with current technology and doesn't require any new insights to make it a reality." "Also, the error correction is fully passive-unwanted error states are quickly repaired by engineered dissipation, without the need for an external computer to watch the circuit and make decisions. "The most interesting thing about my work is that it shows just how simple and small a fully error corrected quantum circuit can be, which is why I call the device the 'Very Small Logical Qubit,'" Kapit told. Rather than actively measuring the system, the new method passively and autonomously suppresses and corrects errors, using relatively simple devices and relatively little computing power. His method takes advantage of a recently discovered unexpected benefit of quantum noise: when carefully tuned, quantum noise can actually protect qubits against unwanted noise. In a new paper published in Physical Review Letters, Eliot Kapit, an assistant professor of physics at Tulane University in New Orleans, has proposed a different approach to quantum error correction. ![]() These approaches typically have a very large overhead, where a large portion of the computing power goes to correcting errors. ![]() Most of them work by repeatedly making measurements on the system to detect errors and then correct the errors before they can proliferate. In order to flip the qubits back to their correct states, physicists have been developing an assortment of quantum error correction techniques. ![]()
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