Moved by
Welcome to Quantumville. Population: uncertain. Walk down Main Street, lined with blurry cars
simultaneously moving and remaining
still. See the house with the curtains
drawn? The television in the living room
is both on and off at the same time. In
this neighborhood, everyday objects do
seemingly contradictory things.
A number of optomechanics teams
have sprung up in recent years, each
cooling its own favorite bit of fairly ordinary stuff. Simmonds works with an aluminum drum (unveiled in the March 10
Nature). In Switzerland, scientists chill
silica doughnuts. At Yale University, sail-like membranes are the vogue.
“We’re putting the mechanics back in
quantum mechanics,” says Yale physicist
Jack Harris.
It’s mainly a race of tortoises creeping
steadily closer to absolute zero, the cold-est of the cold. But recently an interloper
hare took a shortcut to the lead. And the
stakes are high: The winners will test
whether quantum mechanics holds at
ever-larger scales and may go on to build
a new generation of mechanical devices
useful in quantum computing.
Cooling touch
Spend an afternoon watching sunbathers burn at the beach, and the idea of
using light to refrigerate may seem
counterintuitive. But light particles have
a hidden cooling ability that comes from
the tiny nudge they impart when bouncing off an object. This force, too weak for
a beachgoer to feel, is so feeble that sunlight reflecting off a square-meter mirror
delivers a pressure less than a thousandth of the weight of a small paper clip.
“It’s an incredibly tiny effect,” says
physicist Steve Girvin, also of Yale.
In the 1970s scientists figured out
how to use this “radiation pressure” to
cool individual atoms by damping their
vibrations with lasers. Now a slew of new
devices leverage the punch of light and
other forms of electromagnetic energy
to cool objects made of trillions of atoms
or more. This scaled-up cooling doesn’t
suppress the vibrations of individual
atoms. Instead, it quiets the inherent
wobbling of an entire object, like a foot
pressed to a flopping diving board.
Putting light’s cooling power to
work starts with a laser beam bouncing between two mirrors. The distance
between the mirrors in this “optical cavity” determines the frequency of light
that will resonate — just as the length
of a guitar string determines its pitch.
Keep the mirrors still and properly
tuned light will bounce back and forth,
as constant as a metronome.
But allow one of these mirrors to
wobble, and a more intricate and subtle
interplay emerges. A laser beam tuned
below the resonance frequency of the
cavity will push against the swaying mirror and snatch away energy. By stealing
vibrational energy from the mirror, the
bouncing light gets a boost up to the
optical cavity’s stable frequency. Robbed
of energy, the mirror’s swaying weakens,
and it cools.
By measuring the light leaking out
of this type of system, two groups of
