The Argonne National Laboratory of the US Department of Energy (DOE) and the University of Chicago have set a new record for keeping quantum bits (qubits) in a coherent quantum state for more than five seconds. The study, which was published in Science Advances Magazine, is being hailed as a significant step forward in extracting usable work from quantum computers, one that should help quantum computing reach the long-awaited quantum dominance moment.
Coherent states in quantum computing systems are notoriously difficult to sustain. Because of the delicate nature of “ordered chaos,” qubit information and qubit connectivity (entanglement) typically degrade on timescales much shorter than a second. Quantum computing coherency is now available on human-perceivable time scales, thanks to new research. The researchers utilized precision laser pulses to add single electrons to qubits, a technique they call “single-shot readout.”
“[The] emitted light reflects the absence or presence of the electron, and with almost 10,000 times more signal,” said University of Chicago graduate student Elena Glen. “By converting our fragile quantum state into stable electronic charges, we can measure our state much, much more easily. With this signal booster, we can get a reliable answer every time we check what state the qubit is in. This type of measurement is called ‘single-shot readout,’ and with it, we can unlock a lot of useful quantum technologies.”
Single-electron addition is similar to clicking the reset button on a computer, except for quantum states. It removes all previously loaded faults (qubits are sensitive to any external interference), allowing coherent states to “persist.” The goal is to bridge the quantum and electron domains, and the material used is critical: the researchers took advantage of silicon carbide’s intrinsic capabilities in both realms.
“We’ve essentially made a translator to convert from quantum states to the realm of electrons, which are the language of classical electronics, like what’s in your smartphone,” said Chris Anderson of the University of Chicago, co-first author on the paper. “We want to create a new generation of devices that are sensitive to single electrons, but that also host quantum states. Silicon carbide can do both, and that’s why we think it shines.”
While it may not seem like much, in computing, time flows differently; shifting from stable quantum states on the scale of fractions of a second to five seconds improves the amount of useful computing time extracted from the available qubits. Furthermore, it offers up new avenues for expanding processing capacity beyond pure qubit count; the researchers estimate that in that five-second slice, they can complete about 100 million quantum operations.
For a scalable, light-speed distributed quantum computing network, this technique might be used with photonics-based quantum computing. The researchers hope that their findings will pave the way for quantum repeaters to be developed. It is also envisaged that by using silicon carbide, traditional CMOS (Complementary-symmetry Metal Oxide Semiconductor) manufacturing technologies will be able to combine electron spin-based systems into single-charge sensitive electrical devices.
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