Lasers are often used to look at objects in microscopes. But even the best
laser has “quantum noise” that makes a picture blurry and hides the details.
This in turn results in measurements that are less precise than scientists
need. Researchers have designed a new type of microscope that uses squeezed
light to reduce measurement uncertainty. Unlike today’s classical
microscopes, this quantum microscope requires quantum theory to describe its
sensitivity. The microscope uses special “nonlinear” amplifiers to generate
a quantum light source known as squeezed light. This approach enabled a 50
percent improvement in the sensitivity of a specific scientific measurement.
The Impact
Scientists routinely use devices called atomic force microscopes to measure
the properties of materials at the nanoscale. This novel method reduced the
degree of uncertainty in atomic force microscopy. This will result in new
understanding of the properties of materials. With enough squeezing, this
approach can unveil fast electronic interactions that cannot be measured
with a classical microscope. In addition, the squeezed light heats the
microscope much less than a laser would. This is particularly important for
microscopes operated at very low temperatures or for materials that are
sensitive to changes in temperature. Microscopes with reduced uncertainty,
higher speeds, and lower temperatures will open the door to new studies of
quantum materials and quantum devices.
Summary
Quantum microscopy relies on extremely delicate control of light waves.
However, its sensitivity is typically limited by optical losses. In this
research, scientists circumvented the problem with a special type of
entangled light called “squeezed light.” In this case, squeezing means
that the intensities of the light beams are correlated with each other at
the quantum level. Because of this, noise in the measurements is reduced,
thus providing a higher signal to noise ratio. The research performed here
integrated an atomic force microscope microcantilever into a low-loss
nonlinear interferometer that generated squeezing with a four-wave mixing
process. The researchers reduced measurement uncertainty with minimal
heating of the cantilever by taking advantage of low-power squeezed light
and high-power reference signals (the latter never interact with the
microcantilever). By increasing the power in the reference signals and
increasing the squeezing at the same time, it is now possible to achieve a
substantial improvement in microscope sensitivity.
Reference:
Pooser, R. C., et al., Truncated nonlinear interferometry for quantum enhanced
atomic force microscopy, Physical Review Letters 124, 230504 (2020).
DOI: 10.1103/PhysRevLett.124.230504
Tags:
Physics