a state-of-the-art liquid-helium refrigerator capable of achieving millikelvin
temperatures, Cleland’s team put the
wafer in its ground state 93 percent of
the time.
By measuring the electric fields
produced by this object, Cleland and
his colleagues showed that they could
nudge the wafer into a state of superposition — both moving and still at the
same time.
“There can be no doubt that we
achieved superposition,” Cleland says.
This first demonstration of quantum
effects in a fairly ordinary object was
named the 2010 Breakthrough of the
Year by Science.
But Cleland’s sprint to the front of
the pack has some long-term disadvantages. His technique is blind to the actual
position of a fluctuating object, for one
thing, and thus he can’t spot one of the
consequences of quantum mechanics:
zero-point energy, which gives an object
residual motion even in its ground state.
Experimentalists using optomechanics
hope to detect this motion and verify
that it is proportional to how fast an
object normally wobbles.
Back in front
Girding themselves for the long haul,
optomechanics teams have now begun
to catch up to Cleland’s hare strategy.
On March 21 in Dallas at the American
Physical Society meeting, members of
the NIST team presented data showing that their drumlike membrane had
reached the ground state about 60 percent of the time.
The aluminum skin of this drum — in
technical terms, a resonator — moves
up and down much more slowly than
Cleland’s object, vibrating less than
11 million times per second. Reaching
the ground state at this slower wobble
couldn’t be done with Cleland’s refrigerator; it required the cooling nudge of
microwaves.
The payoff for going the extra mile:
time. The slower an object wobbles, the
longer it tends to stay in its ground state.
For Cleland, the ground state lifetime
was about 6 nanoseconds. “The differ-
ence with our system, our resonator, is
that it has a very long lifetime, about 100
microseconds,” says Simmonds. “That’s
the key element that sets it apart.”
With the results unpublished, the
team won’t say whether any quantum
effects have been seen. But the stability
could give the researchers an advantage
for using optomechanical devices to
store and relay information.
A “killer app,” some say, would be
playing interpreter between different
wavelengths of light or other electromagnetic energy. A resonator in its
ground state could theoretically be
designed to absorb photons of just about
any kind of light, stored as packets of
vibrational energy.
Cool the resonator back to its ground
state, and it could release this energy as
light of a different wavelength. So giga-
hertz microwave energy that sets a stick
to wobbling could be reemitted at optical
frequencies hundreds of thousands of
times higher, for instance. Such devices
could bridge quantum computing sys-
tems that use different frequencies of
light to transmit bits of information.
Opto grab bag Light has been used to cool a range of mechanical objects (some highlighted below, from left) in laboratories across the world.
When objects get really cold, some scientists opt to measure temperature in quanta, or packets of vibrational energy, rather than in kelvins.
Stick
UC Santa Barbara
450 micrometers
12,500 hertz
135 millikelvins
