Take that, sports cars! Physicists
at NIST can accelerate their beryllium ions from zero to 100 mph and stop them
in just a few microseconds. What’s more, the ions come to a complete stop and
hardly feel the effects of the ride. And they’re not just good for
submicroscopic racing—NIST physicists think their zippy ions may be useful in
future quantum computers.
The ions travel 100 times faster
than was possible before across a few hundred micrometers in an ion trap—a single
ion can go 370 um in 8 microseconds, to be exact (about 100 mph.)
Although ions can go much faster in
accelerators, the NIST ions demonstrate precision control of fast acceleration
and sudden stops in an ion trap. A close analogy is a marble resting at the
bottom of a bowl, and the bowl suddenly accelerating. During the transport, the
marble will oscillate back and forth relative to the center of the bowl. If the
bowl is suddenly stopped at the right time, the marble will come to rest
together with the bowl. Furthermore, the NIST researchers assured that their
atomic marble’s electron energy levels are not affected, which is important for
a quantum computer, where information stored in these energy levels would need
to be moved around without compromising the information content.
For a quantum computer to solve
important problems that are intractable today, the information carried by many
quantum bits, or qubits, needs to be moved around in the processor. With ion
qubits, this can be accomplished by physically moving the ions. In the past,
moving ions took much longer than the duration of logic operations on the ions.
Now these timescales are nearly equivalent. This reduces processing overhead,
making it possible to move ions and prepare them for reuse much faster than
As described in Physical Review
Letters, NIST researchers cooled trapped ions to their lowest quantum
energy state of motion and, in separate experiments, transported one and two
ions across hundreds of micrometers in a multi-zone trap. Rapid acceleration
excites the ions’ oscillatory motion, which is undesirable, but researchers
controlled the deceleration well enough to return the ions to their original
quantum state when they came to a stop. A research group from Mainz, Germany,
reports similar results.
The secret to the speed and control
is custom electronics. NIST researcher Ryan Bowler used fast FPGA (field-programmable
gate array) technology to program the voltage levels and durations applied to
various electrodes in the ion trap. The smooth voltage supply can move the ions
very fast while also keeping them from getting too excited.
With advances in precision control,
researchers think ions could be transported even more quickly and yet still
return to their original quantum states when they stop. Researchers must also
continue to work on the many practical challenges, such as suppressing unwanted
heating of the ion motion from noisy electric fields in the environment.