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Title: Startup Puts a Logical Qubit In a Single Piece of Hardware

Link: https://hardware.slashdot.org/story/25/06/06/...

Startup Nord Quantique has demonstrated that a single piece of hardware can
host an error-detecting logical qubit by using two quantum frequencies within
one resonator. The breakthrough has the potential to slash the hardware
demands for quantum error correction and deliver more compact and efficient
quantum computing architectures. Ars Technica reports: The company did two
experiments with this new hardware. First, it ran multiple rounds of error
detection on data stored in the logical qubit, essentially testing its
ability to act like a quantum memory and retain the information stored there.
Without correcting errors, the system rapidly decayed, with an error
probability in each round of measurement of about 12 percent. By the time the
system reached the 25th measurement, almost every instance had already
encountered an error. The second time through, the company repeated the
process, discarding any instances in which an error occurred. In almost every
instance, that meant the results were discarded long before they got through
two dozen rounds of measurement. But at these later stages, none of the
remaining instances were in an erroneous state. That indicates that a
successful correction of the errors -- something the team didn't try -- would
be able to fix all the detected problems. Several other companies have
already performed experiments in which errors were detected -- and corrected.
In a few instances, companies have even performed operations with logical
qubits, although these were not sophisticated calculations. Nord Quantique,
in contrast, is only showing the operation of a single logical qubit, so it's
not even possible to test a two-qubit gate operation using the hardware it
has described so far. So simply being able to identify the occurrence of
errors is not on the cutting edge. Why is this notable? All the other
companies require multiple hardware qubits to host a single logical qubit.
Since building many hardware qubits has been an ongoing challenge, most
researchers have plans to minimize the number of hardware qubits needed to
support a logical qubit -- some combination of high-quality hardware, a
clever error correction scheme, and/or a hardware-specific feature that
catches the most common errors. You can view Nord Quantique's approach as
being at the extreme end of the spectrum of solutions, where the number of
hardware qubits required is simply one. From Nord Quantique's perspective,
that's significant because it means that its hardware will ultimately occupy
less space and have lower power and cooling requirements than some of its
competitors. (Other hardware, like neutral atoms, requires lots of lasers and
a high vacuum, so the needs are difficult to compare.) But it also means
that, should it become technically difficult to get large numbers of qubits
to operate as a coherent whole, Nord Quantique's approach may ultimately help
us overcome some of these limits.

Read more of this story at Slashdot.

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