Quantum Zeno Effects: Schrödinger’s Cat Dies Sooner or Later
From Futurity:
You’ve probably heard about Schrödinger’s cat, which famously is trapped
in a box with a mechanism that is activated if a radioactive atom
decays, releasing radiation. The act of looking in the box collapses the
atom’s wave function—the mathematical description of its state—from a
“superposition” of states to a definite state, which either kills the
cat or lets it live another day.
But did you know that if you peek into the cat box
frequently—thousands of times a second—you can either delay the fateful
choice or, conversely, accelerate it? The delay is known as the quantum
Zeno effect and the acceleration as the quantum anti-Zeno effect.
The quantum Zeno effect was named by analogy with the arrow paradox
conceived by the Greek philosopher Zeno: At any given instant of time,
an arrow in flight is motionless; how then can it move? Similarly, if an
atom could be continually measured to see if it is still in its initial
state, it would always be found to be in that state.
Both the Zeno and the anti-Zeno effects are real and happen to real
atoms. But how does this work? How can measurement either delay or
accelerate the decay of the radioactive atom? What is “measurement,”
anyway?
The physicist’s answer is that in order to obtain information about a
quantum system, the system must be strongly coupled to the environment
for a brief period of time. So the goal of measurement is to obtain
information, but the strong coupling to the environment means that the
act of measurement also necessarily disturbs the quantum system.
But what if the system was disturbed but no information was passed to
the outside world? What would happen then? Would the atom still exhibit
the Zeno and anti-Zeno effects?
Kater Murch’s group at Washington University in St. Louis has been
exploring these questions with an artificial atom called a qubit. To
test the role of measurement in the Zeno effects, they devised a new
type of measurement interaction that disturbs the atom but learns
nothing about its state, which they call a “quasimeasurement.”
They report in Physical Review Letters
that quasimeasurements, like measurements, cause Zeno effects.
Potentially the new understanding of the nature of measurement in
quantum mechanics could lead to new ways of controlling quantum systems....MORE
