Caltech’s new fiber-like photonic chips achieve record-low visible-light loss, enabling more coherent lasers and next-generation quantum and sensing technologies.
Category: quantum physics – Page 2
Quantum trembling: Why there are no truly flat molecules
Traditional chemistry textbooks present a tidy picture: Atoms in molecules occupy fixed positions, connected by rigid rods. A molecule such as formic acid (methanoic acid, HCOOH) is imagined as two-dimensional—flat as a sheet of paper. But quantum physics tells a different story. In reality, nature resists rigidity and forces even the simplest structures into the third dimension.
Researchers led by Professor Reinhard Dörner of the Institute for Nuclear Physics at Goethe University have now determined the precise spatial structure of the “flat” formic acid molecule using an X-ray beam from the PETRA III synchrotron radiation source at the DESY accelerator center in Hamburg. They collaborated with colleagues from the universities of Kassel, Marburg and Nevada, the Fritz Haber Institute, and the Max Planck Institute for Nuclear Physics. The study is published in Physical Review Letters.
To accomplish this, they made use of two effects that occur when X-ray radiation strikes a molecule. First, the radiation ejects several electrons from the molecule (photoelectric effect and Auger effect). As a result, the atoms become so highly charged that the molecule bursts apart in an explosion (Coulomb explosion). The scientists succeeded in measuring these processes sequentially, even though they take place within femtoseconds—millionths of a billionth of a second.
Quantum entanglement could link distant telescopes for sharper images
To capture higher-definition and sharper images of cosmological objects, astronomers sometimes combine the data collected by several telescopes. This approach, known as long-baseline interferometry, entails comparing the light signals originating from distant objects and picked up by different telescopes that are at different locations, then reconstructing images using computational techniques.
Conventional long-baseline interferometry methods combine the light signals collected by different telescopes using an interferometer. To do this, however, it relies on delicate optical links that bring light beams together and that are difficult to establish when telescopes are located at long distances from each other.
Researchers at University of Arizona, University of Maryland and NASA Goddard Space Flight Center recently proposed an alternative approach to achieve higher resolution telescopy images that leverages a quantum effect known as entanglement. Their proposed approach, outlined in a paper published in Physical Review Letters, allows distant entangled telescopes, which share a unified quantum state irrespective of how distant they are, to extract the same information about a given scene or cosmological image.
Entangled Ions Measure Time Faster
An optical clock based on a pair of calcium ions achieves a given precision more quickly when the ions are entangled.
What time is it? How precisely you can answer this question might depend on how long you are able to measure. Glance at a clock and you’ll first register the positions of the hour and minute hands. Look for longer and you’ll make out the movement of the second hand, improving your precision 60-fold. The most precise timepieces currently available are state-of-the-art optical clocks, and these also return a more precise result the longer that they are interrogated. But for many applications—in satellite navigation systems, for example, where the position of a fast-moving vehicle needs to be determined quickly—the answer must be prompt as well as precise. Now Kai Dietze at the German National Metrology Institute and colleagues have demonstrated a way to use quantum entanglement to halve the measurement time of an ion-based optical clock without compromising its precision [1].
Optical clocks are the technological successors to microwave atomic clocks, which, for nearly 60 years, have defined the International System of Units (SI) unit of time: the second. Microwave atomic clocks have been refined since they were first invented in the 1950s, but now optical clocks are reaching maturity in the sense that several systems reach or exceed the criteria required by the International Bureau of Weights and Measures for redefining the second. Optical clocks could potentially outperform microwave clocks by 4 orders of magnitude, with implications for fundamental physics and geodesy.
Quantum entanglement pushes optical clocks to new precision
By replacing single atoms with an entangled pair of ions, physicists in Germany have demonstrated unprecedented stability in an optical clock. Publishing their results in Physical Review Letters, a team led by Kai Dietze at the German National Metrology Institute, hope their approach could help usher in a new generation of optical clocks—opening up new possibilities in precision experiments and metrology.
To measure the passing of time, every clock works by counting oscillations of some reference frequency—whether it’s the swinging pendulum of a clocktower, or the vibrations of an electrified quartz crystal in a modern digital clock. Timekeeping accuracy is directly tied to how reliable these oscillations are: while a pendulum can accrue noticeable variations in its swing, vibrating quartz is far more reliable, making quartz clocks far more accurate.
Today, optical clocks are the most precise timekeepers ever achieved. In these devices, atoms are first “probed” by an ultra-stable laser tuned close to a specific optical transition. When the laser frequency matches the energy difference between two electronic states, an electron is excited to a higher energy level.
New chip-scale microcomb uses lithium niobate to generate evenly spaced light
Applied physicists in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have discovered a new way to generate ultra-precise, evenly spaced “combs” of laser light on a photonic chip, a breakthrough that could miniaturize optical platforms like spectroscopic sensors or communication systems.
The research was led by Marko Lončar, the Tiantsai Lin Professor of Electrical Engineering and Applied Physics at SEAS, and published in Science Advances. The paper’s first author is Yunxiang Song, a graduate student in Quantum Science and Engineering.
Quantum simulator reveals statistical localization that keeps most qubit states frozen
In the everyday world, governed by classical physics, the concept of equilibrium reigns. If you put a drop of ink into water, it will eventually evenly mix. If you put a glass of ice water on the kitchen table, it will eventually melt and become room temperature. That concept rooted in energy transport is known as thermalization, and it is easy to comprehend because we see it happen every day. But this is not always how things behave at the smallest scales of the universe.
In the quantum realm—at the atomic and sub-atomic scales—there can be a phenomenon called localization, in which equilibrium spreading does not occur, even with nothing obviously preventing it. Researchers at Duke University have observed this intriguing behavior using a quantum simulator for the first time. Also known as statistical localization, the research could help probe questions about unusual material properties or quantum memory.
The results appear in Nature Physics.
Simplifying quantum simulations—symmetry can cut computational effort by several orders of magnitude
Quantum computer research is advancing at a rapid pace. Today’s devices, however, still have significant limitations: For example, the length of a quantum computation is severely limited—that is, the number of possible interactions between quantum bits before a serious error occurs in the highly sensitive system. For this reason, it is important to keep computing operations as efficient and lean as possible.
Drawing on the example of a quantum simulation, physicists Guido Burkard and Joris Kattemölle from the University of Konstanz illustrate how harnessing symmetry dramatically lowers the computational effort needed: They use recurring patterns in the quantum systems to reduce the required computational effort by a factor of a thousand or more. The method has now been published in the journal Physical Review Letters.
Microscopic mirrors for future quantum networks: A new way to make high-performance optical resonators
Researchers in the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Faculty of Arts and Sciences have devised a new way to make some of the smallest, smoothest mirrors ever created for controlling single particles of light, known as photons. These mirrors could play key roles in future quantum computers, quantum networks, integrated lasers, environmental sensing equipment, and more.
A team from the labs of Marko Lončar, the Tiantsai Lin Professor of Electrical Engineering at SEAS; Mikhail Lukin, the Joshua and Beth Friedman University Professor in the Department of Physics; and Kiyoul Yang, assistant professor of electrical engineering at SEAS; have described their new method for making high-performance, curved optical mirrors in a study published in Optica.
Using two such mirrors to trap light between them, the team demonstrated state-of-the-art optical resonators that can control light at near-infrared wavelengths, which is important for manipulating single atoms in quantum computing applications.
Triplet superconductivity—physicists may have found the missing link for quantum computers
Many physicists are searching for a triplet superconductor. Indeed, we could all do with one, although we may not know it yet—or understand why. Triplet superconductors could be the key to achieving the most energy-efficient technology in the future.
“A triplet superconductor is high on the wish list of many physicists working in the field of solid state physics,” said Professor Jacob Linder. He works at NTNU’s Department of Physics, more specifically at QuSpin—a research center where physicists grapple with some of the gnarliest questions you can imagine. “Materials that are triplet superconductors are a kind of ‘holy grail’ in quantum technology, and more specifically quantum computing,” explained Linder.
He and his colleagues are now on the trail of this triplet superconductor—much to the excitement of physicists worldwide. “We think we may have observed a triplet superconductor,” said Professor Linder.