Physicists have shown a new way to obtain by direct observation the essential details that describe an isolated quantum system like a gas of atoms. The new method provides information about the probability of finding atoms at specific points in the system with unprecedented spatial resolution. With this technique, scientists can obtain details on a scale of ten nanometers – smaller than the width of a virus.
Experiments at the Joint Quantum Institute (JQI), a research partnership between the National Institute of Standards and Technology (NIST) and the University of Maryland, use an optical lattice – a network of laser light that suspends thousands of individual atoms – for probability to determine that an atom is at a particular location. Since every single atom in the lattice behaves like any other, a measurement of the entire atomic group shows the likelihood that a single atom is at a particular point in space.
Published in the journal Physical Review X the JQI technique (and a similar technique that was simultaneously published by a group at the University of Chicago) allows the probability of atomic positions to be well below the wavelength of the Indicate illumination of the atoms of light used – 50 times better than the limit of what optical microscopy can normally resolve.
"This is evidence of our ability to observe quantum mechanics," said Trey Porto of JQI, one of the physicists behind the research effort. "It was not possible to create atoms with nearly this precision."
To understand a quantum system, physicists often talk about its "wave function". It's not just an important detail; It's the whole story. It contains all the information you need to describe the system.
"It's the description of the system," said JQI physicist Steve Rolston, another author of the publication. "When you have the wave function information, you can calculate everything else about it, such as the object's magnetism, its conductivity, and its likelihood of emitting or absorbing light."
While the wave function is a mathematical expression rather than a physical object, the team's method can uncover the behavior that describes the wave function: the probabilities that a quantum system behaves in one way or another. In the world of quantum mechanics, probability is everything.
Among the many strange principles of quantum mechanics is the notion that objects may not have a definable location before measuring their position. The electrons that surround, for example, the atomic nucleus, do not move in regular planetary orbits, contrary to the picture that some of us have learned in school. Instead, they seem like rippling waves, so it can not be said that an electron itself has a specific location. Rather, the electrons are in blurred regions of space.
All objects can exhibit this wavy behavior, but for anything large enough to be seen with the naked eye, the effect is imperceptible and the rules of classical physics are in effect. Make sure that buildings, buckets or bread crumbs spread like waves. But isolate a tiny object like an atom, and the situation is different because the atom exists in a size range where the effects of quantum mechanics are paramount. It is not safe to say where it is, only that it is found somewhere. The wave function returns the set of probabilities by which the atom can be found at a particular location.
Quantum mechanics is well-known to physicists well enough to calculate the wave function for a sufficiently simple system without first considering it. Many interesting systems are complicated, however.
"There are quantum systems that can not be calculated because they are too difficult," Rolston said – molecules that consist of several large atoms. "This approach could help us to understand these situations."
Since the wave function describes only a set of probabilities, how can physicists get a complete picture of their effects in a short time? The team's approach is to measure a large number of identical quantum systems simultaneously and to combine the results into one overall picture. It's like throwing 100,000 pairs of dice simultaneously – each roll yields a single result and adds a single point on the probability curve that shows the values of all the dice.
What the team observed were the positions of the approximately 100,000 atoms Ytterbium floats the optical grating in its lasers. The ytterbium atoms are isolated from their neighbors and restricted to move back and forth along a one-dimensional line segment. In order to get a high-resolution image, the team has found a way to observe narrow slices of these line segments and how often each atom appeared in its respective section. After watching one region, the team measured another until it had the whole picture.
Rolston said he did not yet think of a "killer app" that would exploit the technology, the mere fact that the team has something that is central to quantum science fascinates him directly.
"It's not clear where it's going to be used, but it's a new technology that offers new opportunities," he said. "We've been using an optical grating to capture atoms for years, and now it's a new kind of measurement tool."
Extremely accurate measurements of atomic states for quantum computing
Subhankar, S., et al., Nanoscale Atomic Density Microscopy, Physical Review X (2019). DOI: 10.1103 / PhysRevX.9.021002
Researchers shed new light on the atomic wave function (2019, 16 May)
retrieved on May 16, 2019
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