“Suspended” nanoparticles can push the limits of quantum entanglement

Glass particles suspended in the laser beam can interact (conception diagram). Image credit: Equinox Graphics Ltd.

Recently, a research team led by Benjamin A. Stickler of the University of Duisburg-Essen in Germany suspended tiny glass balls in a vacuum, causing them to interact at close range, enabling precise manipulation of “suspended” nanoparticles, thus opening up new ways to explore the mysterious and ambiguous zone between the everyday world and counterintuitive quantum physics. The findings were published in Science.

Romain Quidant, a physicist at the Swiss Federal Institute of Technology, believes that this is undoubtedly an important milestone in opening up new opportunities. Suspended particles could one day become platforms for quantum computing or pave the way for sophisticated and sensitive measurement devices.

For the first time, the research team tried multiple suspended particles. They reflected the laser light back from the liquid crystal panel in the vacuum chamber, splitting the beam in two. A 200 nm wide glass ball is then injected into the chamber using an ultrasonic atomizer until the nanospheres are captured in the focal point of each of the two laser beams.

This “photospiration” technique works because the rapid oscillation of the laser electric field causes the charge to appear at the opposite ends of each nanosphere at the same speed, like the poles of a bar magnet. This polarization creates a force that pushes the particle towards the area where the light is most intense, pointing to the focal point of the laser beam.

Benjamin A. Stickler explains that when polarization flips back and forth rapidly, it acts like an electric current inside an antenna that emits electromagnetic waves. “Because there is an acceleration charge, it emits radiation.”

By adjusting the LCD panel, the researchers could pull the two focal points closer together. At a distance of a few microns, the particles begin to sense each other’s waves, and the researchers can make them vibrate consistently, like mass connected by a series of springs.

Tweaking the laser also allows the researchers to turn off the force that one particle exerts on another, without turning off the opposite force from the second particle. Stickler said their next step is to use lasers to cool the two particles into a quantum ground state. At that point, it will be possible to place particles in a state of quantum entanglement, meaning that some of their measurable properties are stronger than the correlations allowed by the classical non-quantum laws of physics.

Entanglement is a sign of quantum behavior and is usually only observed at the subatomic scale. Physicists have long debated whether macroscopic objects are governed by their own set of laws, or whether quantum effects are too difficult to observe at these scales. By proving quantum behavior at larger and larger scales, many experiments are working to explore this question. Last year, two teams independently placed a pair of micron-scale barrels entangled, the first such experiment on a macroscopic object.

But the researchers say there are limitations to such “clamped” objects: They are physically connected to devices, making it difficult for subtle quantum states not to be destroyed.

With this in mind, Peter Zoller et al., a theoretical physicist at the University of Innsbruck in Austria, first envisioned quantum experiments using suspended nanoparticles on March 5, 2010. Zoller believes that nanoparticles can be imagined as a small computer that can be controlled and moved with lasers. ”

Stickler added that another advantage of suspension technology is that it can capture more than two particles very well. Zoller agrees: “It can scale to larger quantities immediately. When suspension and laser cooling are applied to individual atoms or ions, it’s like a secret recipe in quantum computing. The same thing happens on nanoparticles. (Source: China Science Daily Xin Yu)

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