A
discovery by physicists at University of California Santa Barbara may
earn silicon carbide––a semiconductor commonly used by the electronics
industry––a role at the center of a new generation of information
technologies designed to exploit quantum physics for tasks such as
ultrafast computing and nanoscale sensing.
The
research team discovered that silicon carbide contains crystal
imperfections that can be controlled at a quantum mechanical level. The
finding is published this week in the journal Nature.
The
research group of David Awschalom, senior author, made the finding.
Awschalom is director of UCSB’s Center for Spintronics & Quantum
Computation, professor of physics, electrical and computer engineering,
and the Peter J. Clarke Director of the California NanoSystems
Institute.
In
conventional semiconductor-based electronic devices, crystal defects
are often deemed undesirable because of their tendency to immobilize
electrons by “trapping” them at a particular crystal location. However,
the UCSB team discovered that electrons that become trapped by certain
imperfections in silicon carbide do so in a way that allows their
quantum states to be initialized, precisely manipulated, and measured
using a combination of light and microwave radiation. This means that
each of these defects meets the requirements for use as a quantum bit,
or “qubit,” which is often described as the quantum mechanical analog of
a transistor, since it is the basic unit of a quantum computer.
“We
are looking for the beauty and utility in imperfection, rather than
struggling to bring about perfect order,” said Awschalom, “and to use
these defects as the basis for a future quantum technology.”
Most
crystal imperfections do not possess these properties, which are
intimately tied to the atomic structure of a defect and the electronic
characteristics of its semiconductor host, explained Awschalom. In fact,
before this research, the only system known to possess these same
characteristics was a flaw in diamond known as the nitrogen-vacancy
center.
The
diamond nitrogen-vacancy center is renowned for its ability to function
as a qubit at room temperature, while many other quantum states of
matter require an extremely cold temperature, near absolute zero.
However, this center exists in a material that is difficult to grow and
challenging to manufacture into integrated circuits.
In
contrast, high-quality crystals of silicon carbide, multiple inches in
diameter, are commonly produced for commercial purposes. They can be
readily fashioned into a multitude of intricate electronic,
optoelectronic, and electromechanical devices. In addition, the defects
studied by Awschalom and his group are addressed using infrared light
that is close in energy to the light used widely throughout modern
telecommunications networks. And while several distinct defect types
were studied at a range of temperatures, two of them were capable of
room temperature operation, just like the diamond nitrogen-vacancy
center.
The
combination of these features makes silicon carbide, with its defects,
an attractive candidate for future work seeking to integrate quantum
mechanical objects with sophisticated electronic and optical circuitry,
according to the researchers. This research fits within a wider effort
at UCSB to engineer quantum devices by fostering collaboration between
the fields of materials science and quantum physics.
While
defects in silicon carbide may offer many technologically attractive
qualities, an immense number of defects in other semiconductors are
still left to be explored.
“Our
dream is to make quantum mechanics fully engineerable,” said William
Koehl, lead author and a graduate student in the Awschalom lab. “Much
like a civil engineer is able to design a bridge based on factors such
as load capacity and length span, we’d like to see a day when there are
quantum engineers who can design a quantum electronic device based on
specifications such as degree of quantum entanglement and quality of
interaction with the surrounding environment.”
Room temperature coherent control of defect spin qubits in silicon carbide
