Tag: quantum mechanics

Measuring time at the quantum level

Measuring time at the quantum level

Physicists using the Swiss Light Source SLS have found a way to measure the time involved in quantum events and found it depends on the symmetry of the material.

“The concept of time has troubled philosophers and physicists for thousands of years, and the advent of quantum mechanics has not simplified the problem,” says Hugo Dil, a physicist at Paul Scherrer Institute PSI and professor at EPFL. “The central problem is the general role of time in quantum mechanics, and especially the timescale associated with a quantum transition.”

Quantum events, like tunnelling, or an electron changing its state by absorbing a photon, happen at mind‑bending speeds. Some take only a few tens of attoseconds (10-18 seconds), which is so short that light would not even cross the width of a small virus.

But measuring time intervals this small is notoriously difficult, also because any external timing tool can distort the very thing we want to observe. “Although the 2023 Nobel prize in physics shows we can access such short times, the use of such an external time scale risks to induce artefacts,” says Dil. “This challenge can be resolved by using quantum interference methods, based on the link between accumulated phase and time.”

Measuring quantum time without an external clock

Dil and his team from EPFL have now led research that has developed a way to accurately measure time in quantum events. When electrons absorb a photon and leave a material, they carry information in the form of their spin, which changes depending on how the underlying quantum process unfolds. By reading these tiny changes, the researchers could infer how long the transition takes, without ever using an external clock.

Read more on the PSI website

Image: Quantum events can unfold on attosecond timescales, making them notoriously difficult to measure. Researchers have now devised a way to measure the duration of quantum transitions without relying on an external clock.

Credit: © EPFL 2026/iStock (bymuratdeniz)

Coherent control of strongly driven quantum dynamics using FERMI shaped pulses

Coherent control of strongly driven quantum dynamics using FERMI shaped pulses

The interaction of light with matter provides indispensable insight into the quantum mechanical world of atoms and molecules on their intrinsic time and length scale. Compared to the macroscopic world, these scales are extreme: about 10 fs for the motion of the nuclei, about 10 as for the motion of the electrons; 0.2 nm is the typical length of a chemical bond. A major objective in science is the control of the nanoscopic processes on their extreme scales, which remains a challenge. Based on the concepts of quantum mechanics, specially tailored light fields can be used to address this problem. Here, the electromagnetic wave-character of light is exploited. By shaping the amplitude, phase and polarization of the electromagnetic waves, fields can be sculpted that enhance certain quantum processes while suppressing others, resulting in a net control of the system. The prerequisite is the ability to shape the electromagnetic field of ultrashort laser pulses with durations of just a few femtoseconds. Such pulses enabled scientists for the first time to trigger and control the atomic and molecular processes on their natural time scale.

In the visible range of the spectrum the spectro-temporal shaping of ultrashort laser pulses is a mature technique. Potential applications can be found in physics, chemistry and material science, for instance in the control of chemical reactions, efficient qubit manipulation, the exploration of complex reaction pathways, and the emergence of new spectroscopy concepts. To date, corresponding concepts in the extreme ultraviolet (XUV) and X-ray regime are hardly explored. The short-wavelength domain provides a perspective to access shorter time and length scales. Extremely short laser pulses with attosecond duration are available in this range, and highly localized inner-shell electrons can be addressed at these photon energies. Thus, extending spectro-temporal pulse shaping to the short-wavelength regime promises the quantum control of matter on unprecedented short time scales and with chemical sensitivity.

Read more on Elettra website

Image: photoelectron spectrum showing the split-up of the energy level in helium and the control of the relative population by shaping the phase of the XUV pulses. Adapted from the original paper, licensed under a Creative Commons Attribution 4.0 International License

Superconducting X-ray laser reaches operating temperature colder than outer space

Superconducting X-ray laser reaches operating temperature colder than outer space

The facility, LCLS-II, will soon sharpen our view of how nature works on ultrasmall, ultrafast scales, impacting everything from quantum devices to clean energy.

Nestled 30 feet underground in Menlo Park, California, a half-mile-long stretch of tunnel is now colder than most of the universe. It houses a new superconducting particle accelerator, part of an upgrade project to the Linac Coherent Light Source (LCLS) X-ray free-electron laser at the Department of Energy’s SLAC National Accelerator Laboratory.

Crews have successfully cooled the accelerator to minus 456 degrees Fahrenheit – or 2 kelvins – a temperature at which it becomes superconducting and can boost electrons to high energies with nearly zero energy lost in the process. It is one of the last milestones before LCLS-II will produce X-ray pulses that are 10,000 times brighter, on average, than those of LCLS and that arrive up to a million times per second – a world record for today’s most powerful X-ray light sources.

“In just a few hours, LCLS-II will produce more X-ray pulses than the current laser has generated in its entire lifetime,” says Mike Dunne, director of LCLS. “Data that once might have taken months to collect could be produced in minutes. It will take X-ray science to the next level, paving the way for a whole new range of studies and advancing our ability to develop revolutionary technologies to address some of the most profound challenges facing our society.”

With these new capabilities, scientists can examine the details of complex materials with unprecedented resolution to drive new forms of computing and communications; reveal rare and fleeting chemical events to teach us how to create more sustainable industries and clean energy technologies; study how biological molecules carry out life’s functions to develop new types of pharmaceuticals; and peek into the bizarre world of quantum mechanics by directly measuring the motions of individual atoms.

A chilling feat

LCLS, the world’s first hard X-ray free-electron laser (XFEL), produced its first light in April 2009, generating X-ray pulses a billion times brighter than anything that had come before. It accelerates electrons through a copper pipe at room temperature, which limits its rate to 120 X-ray pulses per second.

Read more on the SLAC website