For the first time, physicists have built a working version of quantum mechanics without complex numbers — numbers that have been considered essential to the theory for nearly a century.
Complex numbers combine a regular “real” number with an “imaginary” one — a multiple of the square root of-1, represented by the symbol i — into a single value, like 3 + 4i. The square root of-1 doesn’t correspond to any quantity you could count or measure directly (you can’t have negative one apple, for instance), which is why mathematicians call it imaginary.
A new study led by MIT researchers could drive the development of more energy-efficient digital displays—such as flat-screen TVs, augmented and virtual reality headsets, smartphone screens, medical imaging devices and even large-area ambient lighting surfaces—that also generate richer, brighter colors.
The MIT scientists, in collaboration with researchers at Samsung, studied the microscopic changes that occur inside LEDs that use electrically excited quantum dots, which are precisely shaped nanoscale semiconductor particles that emit extremely pure colored light. The research appears in Science Advances.
Quantum dots are currently used in some of the computer and television displays with the best picture quality available. The efficiency of these displays could be further improved, and their manufacturing process further simplified, if the quantum dots could be electrically excited, as was first demonstrated in the quantum dot LED (QD-LED) structures more than 20 years ago.
Proving that one quantum measurement is more powerful than another has long been difficult. Physicists from Heinrich Heine University Düsseldorf, Lund University and the University of Innsbruck have now developed and demonstrated a simple technique to certify that a certain class of measurements has properties that cannot be mimicked by simpler means. Their paper is published in the journal PRX Quantum.
Measurements are central to all quantum technologies. They are said to “collapse” the quantum state they act on, destroying its quantum properties and serving as the bridge to the classical world. Curiously, quantum mechanics allows for measurements that are more general than the ones we can directly associate with classical properties of a system.
These generalized measurements, or POVMs, short for Positive Operator Valued Measures, are not just a mathematical curiosity. They are known to improve performance in tasks like distinguishing between quantum states that would otherwise be indistinguishable, extracting more information from quantum sensors and securing quantum communication.
A number of companies, betting on various architectural approaches, are trying to build the first commercially viable quantum computer capable of significantly outperforming current systems.
Oratomic, which entered the race earlier this year with the goal of developing the first utility-scale quantum computer by the end of the decade, said this week that it has raised $300 million. The massive Series A round was co-led by ARCH Venture Partners, Spark Capital, and Khosla Ventures, with participation from Bezos Expeditions, Index Ventures, General Catalyst, Lowercarbon Capital, Bain Capital, and others.
Founded by Caltech physicists, Oratomic uses lasers, which act as optical tweezers, to hold individual atoms in place as the basis for its quantum computer.
Modern life depends on quantum physics. It makes technologies such as GPS navigation, MRI scanners and computer chips possible. Now, the same science may also lead to a new way to test the health of our eyes. A University at Buffalo-led team has used a technique from quantum optics to make a little-known visual pattern produced inside the eye easier to see—potentially opening the door to a new way to test retinal health.
Known as Boehm’s brushes, these faint, two-lobed, bowtie-shaped patterns sometimes appear in peripheral vision when polarized light scatters off structures in the retina. Because people with retinal disease may be less likely to perceive them, scientists have long wondered whether they could serve as a biomarker of retinal health.
However, Boehm’s brushes are often too hard to see, even for people with healthy eyes, to be useful in clinical practice.
A team of researchers at the University of Ottawa and its Nexus for Quantum Technologies Institute, in collaboration with researchers from Federico II University in Italy, has developed a programmable quantum simulator that shapes a beam of light to replicate how particles move through complex materials, avoiding the need for ever-larger electronic hardware.
The work lays the foundation to build a new platform to explore phenomena that could power devices capable of transporting and grouping electrical signals and quantum states in ways not traditionally achievable without relying on optical or engineered systems. The team detailed its findings in a paper published in Science Advances.
Non-Hermitian physics refers to systems that exhibit behaviors not found in conventional physical models, explained Morteza Kayyalha, assistant professor of electrical engineering at Penn State and corresponding author on the paper. These systems can display unusual behaviors, such as enhanced responses to perturbations and external stimuli. They can also demonstrate the non-Hermitian skin effect, where quantum states—which researchers can use to predict the physical properties of a material—become concentrated near a specific boundary or point in the material, rather than spreading uniformly throughout.
Underpinning much of modern technology, from smartphones to scanning tunneling microscopes to particle colliders, is Fermi’s Golden Rule. Named for 20th-century Italian American physicist Enrico Fermi (but actually discovered by British physicist Paul Dirac), the rule is a formula that connects what can be measured in an experiment—such as how fast atoms “jump” between energy states—to the microscopic properties of a quantum mechanical system. The formula is taught in every undergraduate quantum physics class.
Yet scientists sometimes misapply it. They either misjudge the conditions under which the formula works, or they miss the “window” for its use. A “user manual” for Fermi’s Golden Rule would be a boon to researchers, says Yale physicist Nir Navon—and now he and his lab partners have provided one.
“We put one of the most famous formulas in all of quantum mechanics to the test, and found where it works and where it fails, including ways that many physicists weren’t fully aware of,” said Navon, an associate professor of physics in Yale’s Faculty of Arts and Sciences and senior author of a new study published in the journal Nature Physics. “We’re telling everyone who uses it to take a breath first and check their ingredients.”