New detector breakthrough pushes boundaries of quantum computing
A new article shows potential for graphene bolometers to become a game- changer for quantum technology

Date:
September 30, 2020
Source:
Aalto University
Summary:
A new article shows potential for graphene bolometers to become
a game- changer for quantum technology.



FULL STORY ========================================================================== Physicists at Aalto University and VTT Technical Research Centre of
Finland have developed a new detector for measuring energy quanta
at unprecedented resolution. This discovery could help bring quantum
computing out of the laboratory and into real-world applications. The
results have been published today in Nature.


==========================================================================
The type of detector the team works on is called a bolometer, which
measures the energy of incoming radiation by measuring how much it
heats up the detector. Professor Mikko Mo"tto"nen's Quantum Computing
and Devices group at Aalto has been developing their expertise in
bolometers for quantum computing over the past decade, and have now
developed a device that can match current state-of-the-art detectors
used in quantum computers.

'It is amazing how we have been able to improve the specs of our bolometer
year after year, and now we embark on an exciting journey into the world
of quantum devices,' says Mo"tto"nen.

Measuring the energy of qubits is at the heart of how quantum computers operate. Most quantum computers currently measure a qubit's energy
state by measuring the voltage induced by the qubit. However, there
are three problems with voltage measurements: firstly, measuring the
voltage requires extensive amplification circuitry, which may limit the scalability of the quantum computer; secondly, this circuitry consumes a
lot of power; and thirdly, the voltage measurements carry quantum noise
which introduces errors in the qubit readout. Quantum computer researchers
hope that by using bolometers to measure qubit energy, they can overcome
all of these complications, and now Professor Mo"tto"nen's team have
developed one that is fast enough and sensitive enough for the job.

'Bolometers are now entering the field of quantum technology and perhaps
their first application could be in reading out the quantum information
from qubits.

The bolometer speed and accuracy seems now right for it,' says Professor Mo"tto"nen.

The team had previously produced a bolometer made of a gold-palladium
alloy with unparalleled low noise levels in its measurements, but it was
still too slow to measure qubits in quantum computers. The breakthrough
in this new work was achieved by swapping from making the bolometer out
of gold-palladium alloys to making them out of graphene. To do this,
they collaborated with Professor Pertti Hakonen's NANO group -- also
at Aalto University -- who have expertise in fabricating graphene-based devices. Graphene has a very low heat capacity, which means that it is
possible to detect very small changes in its energy quickly. It is this
speed in detecting the energy differences that makes it perfect for a
bolometer with applications in measuring qubits and other experimental
quantum systems. By swapping to graphene, the researchers have produced
a bolometer that can make measurements in well below a microsecond,
as fast as the technology currently used to measure qubits.

'Changing to graphene increased the detector speed by 100 times, while
the noise level remained the same. After these initial results, there is
still a lot of optimisation we can do to make the device even better,'
says Professor Hakonen.

Now that the new bolometers can compete when it comes to speed, the
hope is to utilise the other advantages bolometers have in quantum
technology. While the bolometers reported in the current work performs
on par with the current state- of-the-art voltage measurements, future bolometers have the potential to outperform them. Current technology is
limited by Heisenberg's uncertainty principle: voltage measurements will
always have quantum noise, but bolometers do not. This higher theoretical accuracy, combined with the lower energy demands and smaller size -- the graphene flake could fit comfortably inside a single bacterium -- means
that bolometers are an exciting new device concept for quantum computing.

The next steps for their research is to resolve the smallest energy
packets ever observed using bolometers in real-time and to use the
bolometer to measure the quantum properties of microwave photons,
which not only have exciting applications in quantum technologies such
as computing and communications, but also in fundamental understanding
of quantum physics.

Many of the scientists involved in the researchers also work at IQM,
a spin-out of Aalto University developing technology for quantum
computers. "IQM is constantly looking for new ways to enhance its quantum-computer technology and this new bolometer certainly fits the
bill," explains Dr Kuan Yen Tan, Co- Founder of IQM who was also involved
in the research.


========================================================================== Story Source: Materials provided by Aalto_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. R. Kokkoniemi, J.-P. Girard, D. Hazra, A. Laitinen, J. Govenius,
R. E.

Lake, I. Sallinen, V. Vesterinen, M. Partanen, J. Y. Tan,
K. W. Chan, K.

Y. Tan, P. Hakonen, M. Mo"tto"nen. Bolometer operating at the
threshold for circuit quantum electrodynamics. Nature, 2020; 586
(7827): 47 DOI: 10.1038/s41586-020-2753-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200930114207.htm

--- up 5 weeks, 2 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)