Greg Fuchs in the laboratory. |
Physicists
working at the Univ. of California, Santa Barbara and the
Univ. of Konstanz in Germany have developed a breakthrough in the
use of diamond in quantum physics, marking an important step toward
quantum computing. The results are reported in Nature Physics.
The
physicists were able to coax the fragile quantum information contained
within a single electron in diamond to move into an adjacent single
nitrogen nucleus, and then back again using on-chip wiring.
“This
ability is potentially useful to create an atomic-scale memory element
in a quantum computer based on diamond, since the subatomic nuclear
states are more isolated from destructive interactions with the outside
world,” said David Awschalom, senior author.
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.
Awschalom
said the discovery shows the high-fidelity operation of a quantum
mechanical gate at the atomic level, enabling the transfer of full
quantum information to and from one electron spin and a single nuclear
spin at room temperature. The process is scalable, and opens the door to
new solid-state quantum device development.
Scientists
have recently shown that it is possible to synthesize thousands of
these single electron states with beams of nitrogen atoms, intentionally
creating defects to trap the single electrons.
“What
makes this demonstration particularly exciting is that a nitrogen atom
is a part of the defect itself, meaning that these sub-atomic memory
elements automatically scale with the number of logical bits in the
quantum computer,” said lead author Greg Fuchs, a postdoctoral fellow at
UCSB.
Rather
than using logical elements like transistors to manipulate digital
states like “0” or “1,” a quantum computer needs logical elements
capable of manipulating quantum states that may be “0” and “1” at the
same time. Even at ambient temperature, these defects in diamond can do
exactly that, and have recently become a leading candidate to form a
quantum version of a transistor.
However,
there are still major challenges to building a diamond-based quantum
computer. One of these is finding a method to store quantum information
in a scalable way. Unlike a conventional computer, where the memory and
the processor are in two different physical locations, in this case they
are integrated together, bit-for-bit.
“We
knew that the nitrogen nuclear spin would be a good choice for a
scalable quantum memory––it was already there,” said Fuchs. “The hard
part was to transfer the state quickly, before it is lost to
decoherence.”
Awschalom
explained: “A key breakthrough was to use a unique property of quantum
physics––that two quantum objects can, under special conditions,
become mixed to form a new composite object.” By mixing the quantum spin
state of the electrons in the defect with the spin state of the
nitrogen nucleus for a brief time––less than 100 billionths of a
second––information that was originally encoded in the electrons is
passed to the nucleus.
“The
result is an extremely fast transfer of the quantum information to the
long-lived nuclear spin, which could further enhance our capabilities to
correct for errors during a quantum computation,” said co-author Guido
Burkard, a theoretical physicist at the Univ. of Konstanz, who
developed a model to understand the storage process.
The fourth author of the paper is Paul V. Klimov, a graduate student at UCSB.
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2026.html
