Researchers set record by preserving quantum states for more than 5
seconds
Breakthrough using common material could pave way for new quantum
technologies

Date:
February 2, 2022
Source:
DOE/Argonne National Laboratory
Summary:
A team of researchers has maintained a qubit coherence time for
a record five seconds. The qubits are made from silicon carbide,
widely found in lightbulbs, electric vehicles and high voltage
electronics.



FULL STORY ========================================================================== Quantum science holds promise for many technological applications, such
as building hackerproof communication networks or quantum computers
that could accelerate new drug discovery. These applications require
a quantum version of a computer bit, known as a qubit, that stores
quantum information.


==========================================================================
But researchers are still grappling with how to easily read the
information held in these qubits and struggle with the short memory
time, or coherence, of qubits, which is usually limited to microseconds
or milliseconds.

A team of researchers at the U.S. Department of Energy's (DOE) Argonne
National Laboratory and the University of Chicago have achieved two
major breakthroughs to overcome these common challenges for quantum
systems. They were able to read out their qubit on demand and then keep
the quantum state intact for over five seconds -- a new record for this
class of devices. Additionally, the researchers' qubits are made from
an easy-to-use material called silicon carbide, which is widely found
in lightbulbs, electric vehicles and high- voltage electronics.

"It's uncommon to have quantum information preserved on these human timescales," said David Awschalom, senior scientist at Argonne National Laboratory, director of the Q-NEXT quantum research center, Liew Family Professor in Molecular Engineering and Physics at the University of
Chicago, and principal investigator of the project. "Five seconds is
long enough to send a light speed signal to the moon and back. That's
powerful if you're thinking about transmitting information from a qubit
to someone via light. That light will still correctly reflect the qubit
state even after it has circled the Earth almost 40 times -- paving
the way to make a distributed quantum internet." By creating a qubit
system that can be made in common electronics, the researchers hope to
open a new avenue for quantum innovation using a technology that is both scalable and cost-effective.

"This essentially brings silicon carbide to the forefront as a quantum communication platform," said University of Chicago graduate student
Elena Glen, co-first author on the paper. "This is exciting because it's
easy to scale up, since we already know how to make useful devices with
this material." The findings were published on Feb. 2 in the journal
Science Advances.



========================================================================== '10,000 times more signal' The first breakthrough for the researchers
was to make the silicon carbide qubits easier to read.

Every computer needs a way to read information encoded into its bits. For semiconductor qubits, like the ones measured by the team, the typical
readout method is to address the qubits with lasers and measure the
light emitted back.

This procedure is challenging, however, because it requires detecting
single particles of light called photons very efficiently.

Instead, the researchers use carefully designed laser pulses to add a
single electron to their qubit depending on its initial quantum state,
either zero or one. Then the qubit is read out in the same way as before
-- with a laser.

"Only now, the emitted light reflects the absence or presence of the
electron, and with almost 10,000 times more signal," Glen said. "By
converting our fragile quantum state into stable electronic charges,
we can measure our state much, much more easily. With this signal boost,
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." Armed with
the single shot readout method, the scientists could focus on making
their quantum states last as long as possible -- a notorious challenge
for quantum technologies, because qubits easily lose their information
due to noise in their environment.



==========================================================================
The researchers grew highly purified samples of silicon carbide that
reduced the background noise that tends to interfere with their qubit functioning.

Then, by applying a series of microwave pulses to the qubit, they extended
the amount of time that their qubits preserved their quantum information,
a concept referred to as "coherence." "These pulses decouple the qubit
from noise sources and errors by rapidly flipping the quantum state,"
said Chris Anderson of the University of Chicago, co-first author on the
paper. "Each pulse is like hitting the undo button on our qubit, erasing
any error that may have happened between pulses." The researchers think
that even longer coherences should be possible. Extending coherence
time has significant ramifications, such as how complex an operation
a future quantum computer can handle or how small a signal a quantum
sensor can detect.

"For example, this new record time means we can perform over 100 million quantum operations before our state gets scrambled," Anderson said.

The scientists see multiple potential applications for the techniques
they developed.

"The ability to perform single shot readout unlocks a new opportunity:
using the light emitted from silicon carbide qubits to help develop
a future quantum internet," Glen said. "Essential operations such as
quantum entanglement, where the quantum state of one qubit can be known
by reading out the state of another, are now in the cards for silicon carbide-based systems." "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," Anderson said. "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 really shines." The research used resources
of the UChicago Materials Research Science and Engineering Center,
the Pritzker Nanofabrication Facility and the Research Computing Center.

This work was supported by the DOE Office of Basic Energy Sciences,
Materials Science and Engineering division, DOE National Quantum
Information Science Research Centers, the National Science Foundation,
Boeing, Swedish Research Council, Japan Society for the Promotion of
Science, European Commission, Air Force Office of Scientific Research
and Knut and Alice Wallenberg Foundation.

-- Writing contributed by Elena Glen, Chris Anderson and Louise Lerner ========================================================================== Story Source: Materials provided by DOE/Argonne_National_Laboratory. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Christopher P. Anderson, Elena O. Glen, Cyrus Zeledon, Alexandre
Bourassa, Yu Jin, Yizhi Zhu, Christian Vorwerk, Alexander L. Crook,
Hiroshi Abe, Jawad Ul-Hassan, Takeshi Ohshima, Nguyen T. Son,
Giulia Galli, David D. Awschalom. Five-second coherence of a single
spin with single-shot readout in silicon carbide. Science Advances,
2022; 8 (5) DOI: 10.1126/sciadv.abm5912 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220202153853.htm

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