Researchers have succeeded in obtaining a detailed understanding of the microscopic interaction processes which lead to back-action, and have found that back-action components can cancel each other out.

The
ongoing miniaturization trend in computer technologies, which is driven
by cost efficiency and performance demands, will soon reach its limit.
The development of a so-called quantum computer offers a possible
alternative, as it opens up the prospect of achieving much higher
efficiencies by using quantum algorithms. For instance, the quantum
mechanical states of single electrons could replace classical
transistors. However, quantum states are very fragile and are even more
susceptible to back-action than traditional computers. So how realistic
is the idea of the quantum computer?

Making quantum effects visible

LMU-physicist
Dr. Stefan Ludwig and his colleagues have experimentally detected and
theoretically modeled back-action at the quantum level. The scientists
made back-action on single electrons directly visible by taking
advantage of quantum effects. Moreover, they discovered a way of
utilizing fundamental quantum effects to minimize its undesirable
effects. This breakthrough was achieved in collaboration with two
Canadian groups.

Interplay between detector and transistor

The
researchers succeeded in obtaining a detailed understanding of the
microscopic interaction processes which lead to back-action: The
single-electron transistor they used consists of an electron confined
within two adjacent wells. The detector measures whether the electron is
presently in one or the other well. Here is where the back-action
effect comes into play: In a simple picture, detector and transistor
mutually affect each other. Consequently, the detection process itself
modifies the state to be detected. This in turn changes the outcome of
the measurement. In the specific setup used here, the interplay between
detector and single-electron transistor is governed by a complex
combination of charge fluctuations and sound waves.

“One
of our main findings is that different back-action components can
cancel each other out by destructive interference,” says Ludwig, a
member of the Nanosystems Initiative Munich (NIM). “Indeed, the
back-action process itself causes these quantum interferences. This
could be harnessed as a new method for minimizing measurement
back-action and can be seen as a milestone in our efforts to use quantum
physics for computation in the future.”

Quantum interference and phonon-mediated back-action in lateral quantum dot circuits

Source: Nanosystems Initiative Munich