An illustration showing a 3D figure surrounded by infrared rays. Milad Fakurian/Unsplash
A new study that breaks the rules of Heisenberg’s uncertainty principle reveals that qubits can be measured using nanobolometers (highly sensitive sensors that can detect infrared radiation even with slight temperature changes).
For those of you who don’t know what a qubit is, here is a simple explanation. Just like how bits are the most basic unit of information in traditional computers, a qubit is the smallest unit of data in quantum computing.
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It is crucial to measure qubits. Otherwise, scientists won’t be able to process the information in a quantum computer. They also won’t be able to perform calculations or verify any data in the quantum systems if they are unable to read it.
“Measuring the state of a qubit is a key fundamental operation of a quantum computer,” the study authors note.
For instance, “qubit readout in a quantum computer is required to determine the result at the end of a computation as well as for error correction, which is necessary for fault tolerance,” they added.
The traditional process of measuring qubits
Qubits are currently measured using parametric amplifiers, special devices that detect weak signals from a cubit and then amplify the signals to make the information readable. However, this approach has various limitations.
For instance, the amplification of a signal adds a lot of noise. This noise makes it difficult to read the qubit and can result in inaccurate measurements.
Also, “Parametric amplifiers can offer high gain and low noise but introduce challenges in terms of scaling to large numbers of qubits. These challenges include narrow bandwidth, which is undesirable in multiplexed qubit readout.”
When dealing with a large number of qubits, a user needs a device with a wider wavelength so they can detect and measure multiple signals at once.
Additionally, while measuring large amounts of quantum information, parametric amplification may result in signal loss due to large volumes of unwanted noise.
The study authors show that nanobolometers can overcome these limitations, work as an alternative to parametric amplifiers, and achieve “single-shot-readout of superconducting qubits.”
How does a nanobolometer work?
The noise produced by a parametric amplifier represents Heisenberg’s uncertainty principle.
It’s a popular concept of quantum mechanics that suggests that one can not precisely calculate the position or speed of a particle, the position and momentum of a signal, or the voltage and current of a device.
The more accurate you know about one of these variables, the more uncertain you are about the other in the pair. Therefore, the noise in a qubit reading represents inaccuracy or uncertainty.
However, nanobolometers don’t follow this principle. Unlike amplifiers, they detect the number of photons emitted by qubits. So in a way, they are sensing both power (photons) and frequency (number of photons) but from a single source.
“A bolometer requires only a single continuous probe tone with two parameters—power and frequency—to optimize performance. It is not bound to add quantum noise stemming from the Heisenberg uncertainty principle,” the study authors note.
The vacuum noise does not promote detection events in the bolometer since no energy can be extracted from a vacuum.”
Moreover, compared to a parametric amplifier, a nanobolometer is 100 times smaller, can fit inside a bacterium, and requires 10,000 times less power.
The researchers will now further improve the device for better performance.
“With minor modifications, we could expect to see bolometers approaching the desired 99.9% single-shot fidelity in 200 nanoseconds,” András Gunyhó, first author of the study and a doctoral researcher at Aalto University, said.
“We can achieve a smaller and simpler measurement device that makes scaling up to higher qubit counts more feasible.”
The study is published in the journal Nature Electronics.
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