NIST Researchers Create ‘Quantum Cats’ Made of Light

Researchers at the National Institute of Standards and Technology
(NIST) have created "quantum cats" made of photons (particles of
light), boosting prospects for manipulating light in new ways to enhance
precision measurements as well as computing and communications based on
quantum physics.

NIST research associate Thomas Gerrits at the laser table used to create "quantum cats" made of light. Credit: NIST View hi-resolution image

The NIST experiments, described in a forthcoming paper,* repeatedly
produced light pulses that each possessed two exactly opposite
properties—specifically, opposite phases, as if the peaks of the light
waves were superimposed on the troughs. Physicists call this an optical
Schrödinger's cat. NIST's quantum cat is the first to be made by
detecting three photons at once and is one of the largest and most
well-defined cat states ever made from light. (Larger cat states have
been created in different systems by other research groups, including
one at NIST.)

A "cat state" is a curiosity of the quantum world, where particles
can exist in "superpositions" of two opposite properties simultaneously.
Cat state is a reference to German physicist Erwin Schrödinger's famed
1935 theoretical notion of a cat that is both alive and dead
simultaneously.

"This is a new state of light, predicted in quantum optics for a long
time," says NIST research associate Thomas Gerrits, lead author of the
paper. "The technologies that enable us to get these really good results
are ultrafast lasers, knowledge of the type of light needed to create
the cat state, and photon detectors that can actually count individual
photons."

These colorized plots of electric field values indicate how closely the NIST "quantum cats" (left) compare with theoretical predictions for a cat state (right). The purple spots and alternating blue contrast regions in the center of the images indicate the light is in the appropriate quantum state. Credit: Gerrits/NIST View hi-resolution image

The NIST team created their optical cat state by using an ultrafast
laser pulse to excite special crystals to create a form of light known
as a squeezed vacuum, which contains only even numbers of photons. A
specific number of photons were subtracted from the squeezed vacuum
using a device called a beam splitter. The photons were identified with a
NIST sensor that efficiently detects and counts individual photons (see
"NIST Detector Counts Photons With 99 Percent Efficiency," NIST Tech Beat, Apr. 13, 2010, at www.nist.gov/eeel/optoelectronics/detector_041310.cfm.)
Depending on the number of subtracted photons, the remaining light is
in a state that is a good approximation of a quantum cat says
Gerrits—the best that can be achieved because nobody has been able to
create a "real" one, by, for instance, the quantum equivalent to
superimposing two weak laser beams with opposite phases.

NIST conducts research on novel states of light because they may
enhance measurement techniques such as interferometry, used to measure
distance based on the interference of two light beams. The research also
may contribute to quantum computing—which may someday solve some
problems that are intractable today—and quantum communications, the most
secure method known for protecting the privacy of a communications
channel. Larger quantum cats of light are needed for accurate
information processing.

Media Contact: Laura Ost, laura.ost@nist.gov, 303-497-4880