Quantum light ejects noise from microscopy signals

ORNL researchers have developed a quantum, or squeezed, lightweight approach to atomic force microscopy that enables the measurement of signals otherwise buried by noise. Credit: Rafael Poser, ORNL, US Department of Energy

Researchers at Oak Ridge National Laboratory of the Department of Energy used quantum optics to advance state-of-the-art microscopy and illuminate a path to detect physical properties with greater sensitivity than with conventional equipment.

“We showed how lower light is used – as a practical resource for microscopy,” said Ben Laurie of the Materials Science and Technology Division of ORNL. “We measured the displacement of an atomic force microscope microcontroller with better sensitivity than the standard quantum limit.”

Unlike today’s classical microscopes, Poser and Laurie’s quantum microscope requires quantum theory to describe its sensitivity. Nonlinear amplifiers in ORNL’s microscope produce a special quantum light source known as lower light.

“Imagine a blurry picture,” Poser said. “It’s noisy and some fine details are hidden. Classical, noisy lighting prevents you from seeing those details. The ‘squeezed’ version is less blurred and reveals finer details that we couldn’t see due to the noise . ” “We can use a squeezed light source instead of a laser to reduce noise in our sensor readouts,” he said.

The microcontroller of an atomic force microscope is a miniature diving board that physically scans a sample and bends when it senses physical changes. Student interns Nick Savino, Emma Batson, Jeff Garcia and Jacob Becky, Laurie and Poser showed that the quantum microscope they invented could measure the displacement of a microcontroller with a 50% better sensitivity than is classically possible . For each other of long measurements, the quantum-enhanced sensitivity was 1.7 womanometers – about twice the diameter of a carbon nucleus.

“Squeeze light sources have been used to provide quantum-enhanced sensitivity to detect gravitational waves generated by black hole mergers,” Poser said. “Our work is helping translate these quantum sensors from the scale of the universe to the nanoscale.”

His approach to quantum microscopy relies on the control of light waves. When the waves combine, they can interfere constructively, meaning that the amplitudes of the peaks add up to make the resulting wave larger. Or they can interfere destructively, which means that the trough amplitude decreases with the peak amplitude resulting in a smaller wave. This effect can be seen in the waves in the pond or in the electromagnetic wave of light like a laser.

“The interferometer splits and then mixes two light keys to measure small changes in phase that affect the interference of the two beams when they are recombined,” Laurie said. “We employed nonlinear interferometers, which use nonlinear optical amplifiers, to achieve inhomogeneous and inhomogeneous inhomogeneous sensitivity.”

Interdisciplinary Studies, published in Physical review letter, Is the first practical application of nonlinear interferometry.

A well-known aspect of quantum mechanics, the Heisenberg uncertainty principle, makes it impossible to define both the position and the motion of a particle with absolute certainty. A similar uncertainty exists for the amplitude and phase of the light.

This fact creates a problem for sensors that rely on classical light sources such as lasers: the highest sensitivity they can achieve is the Heisenberg uncertainty relation with the same uncertainty in each variable. The squeezed light source reduces the uncertainty in one variable while increasing the uncertainty in the other variable, thus “squeezing” the uncertainty distribution. For that reason, the scientific community has used squeeze to study both great and small phenomena.

Sensitivity in such quantum sensors is usually limited by optical losses. “Squeezed states are fragile quantum states,” Poser said. “In this experiment, we were able to circumvent the problem by exploiting the properties of entanglement.” Entanglement means dealing with independent things. Einstein called it “spooky action at a distance”. In this case, the intensity of the light rays is correlated with each other at the quantum level.

“Because of entanglement, if we measure the power of one beam of light, it will allow us to predict the power of another without measurement,” he said. “Because of entanglement, the noise in these measurements is low, and it provides us with a high signal to noise ratio.”

ORNL’s approach to quantum microscopy is broadly relevant to any optimized sensor that traditionally uses lasers for signal readout. “For example, traditional interferometers can be replaced by nonlinear interferometry to achieve quantum-enhanced sensitivity for biochemical sensing, dark matter detection, or characterization of the magnetic properties of materials,” Laurie said.

The paper is titled “Quantum Anomnear Interferometry for Quantum Enhanced Atomic Force Microscopy.”

ORNL report method that takes quantum sensing to a new level

more information:
RC Pussar et al., Nuclear Nonlinear Interferometry for Quantum-Enhanced Atomic Force Microscopy, Physical review letter (2020). DOI: 10.1103 / PhysRevLett.124.230504

Provided by Oak Ridge National Laboratory

Quotes: Quantum light microscopy removes the noise of the signal (2020, 8 September) from https://phys.org/news/2020-09-quantum-noise-microscopy.html by 8 September 2020.

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