MIT physicists have performed an idealized version of one of the most famous experiments in quantum physics. Their findings demonstrate, with atomic-level precision, the dual yet evasive nature of light. They also happen to confirm that Albert Einstein was wrong about this particular quantum scenario.

The experiment in question is the double-slit experiment, which was first performed in 1801 by the British scholar Thomas Young to show how light behaves as a wave. Today, with the formulation of quantum mechanics, the double-slit experiment is now known for its surprisingly simple demonstration of a head-scratching reality: that light exists as both a particle and a wave. Stranger still, this duality cannot be simultaneously observed. Seeing light in the form of particles instantly obscures its wave-like nature, and vice versa.

The original experiment involved shining a beam of light through two parallel slits in a screen and observing the pattern that formed on a second, faraway screen. One might expect to see two overlapping spots of light, which would imply that light exists as particles, a.k.a. photons, like paintballs that follow a direct path. But instead, the light produces alternating bright and dark stripes on the screen, in an interference pattern similar to what happens when two ripples in a pond meet. This suggests light behaves as a wave. Even weirder, when one tries to measure which slit the light is traveling through, the light suddenly behaves as particles and the interference pattern disappears.

Quantum mechanics is generally regarded as the physical theory that is our best candidate for a fundamental and universal description of the physical world. The conceptual framework employed by this theory differs drastically from that of classical physics. Indeed, the transition from classical to quantum physics marks a genuine revolution in our understanding of the physical world.

One striking aspect of the difference between classical and quantum physics is that whereas classical mechanics presupposes that exact simultaneous values can be assigned to all physical quantities, quantum mechanics denies this possibility, the prime example being the position and momentum of a particle. According to quantum mechanics, the more precisely the position (momentum) of a particle is given, the less precisely can one say what its momentum (position) is. This is (a simplistic and preliminary formulation of) the quantum mechanical uncertainty principle for position and momentum. The uncertainty principle played an important role in many discussions on the philosophical implications of quantum mechanics, in particular in discussions on the consistency of the so-called Copenhagen interpretation, the interpretation endorsed by the founding fathers Heisenberg and Bohr.

This should not suggest that the uncertainty principle is the only aspect of the conceptual difference between classical and quantum physics: the implications of quantum mechanics for notions as (non)-locality, entanglement and identity play no less havoc with classical intuitions.

Researchers investigating atomic-scale phenomena impacting next-generation electronic and quantum devices have captured the first microscopy images of atomic thermal vibrations, revealing a new type of motion that could reshape the design of quantum technologies and ultrathin electronics.

Yichao Zhang, an assistant professor in the University of Maryland Department of Materials Science and Engineering, has developed an electron microscopy technique to directly image “moiré phasons”—a physical phenomenon that impacts superconductivity and heat conduction in two-dimensional materials for next-generation electronic and quantum devices.

A paper about the research, which documents images of the thermal vibration of individual atoms for the first time, has been published in the journal Science.

A research team led by TU Darmstadt has transformed a difficult problem in quantum physics into a much simpler version through innovative reformulation—without losing any important information. The scientists have thus developed a new method for better understanding and predicting difficult quantum mechanical systems. The study is published in Physical Review Letters.

This problem has long preoccupied quantum physics: How can systems consisting of many atoms, between which strong attractive forces act, be described mathematically? Already for about 10 particles, such systems are at the limits of current numerical methods.

It becomes particularly complicated when the atoms are exposed to an external force. However, this is the case in many experiments with cold atoms due to the way in which motion is restricted to one dimension, for example. Such systems of strongly interacting particles in one dimension were proposed in the 1960s and have since served as a reference problem in theoretical physics. So far, they have only been solved in a few special cases.