Possibility of measuring time without Using a Clock

When light illuminates on specific substances, it causes them to release electrons. This is known as ‘photoemission’ and it was introduced by Albert Einstein in 1905, winning him the Nobel Prize. But only in the last couple of years, with advancements in laser technology, have researchers been able to approach the incredibly short timescales of photoemission.

Scientists at EPFL have now illustrated a delay on one billionth of a second in photoemission by estimating the spin of photo emitted electrons without the requirement of ultrashort laser pulses. Photoemission has proven to be a vital procedure, forming a platform for cutting-edge spectroscopy methods that enable researchers to study the properties of electrons in a solid. One such property is spin, an intrinsic quantum property of particles that makes them look like as if they were revolving around their axis.

The extent to which this axis is aligned towards a specific direction is referred to as spin polarization, which is what gives some substances, like iron, magnetic properties. Although, there has been huge progress in using photoemission and spin polarization of photo-emitted electrons, the time scale wherein the entire procedure takes places have not been explored in great detail. The common assumption is that, once light extends the material, electrons are regularly emitted and excited. But more recent researches employing advanced laser technology have challenged this, revealing that there is actually a time delay on the scale of attoseconds.

The laboratory of Hugo Dil at EPFL, with team members in Germany revealed that during photoemission, the spin polarization of emitted electrons can be linked to the attosecond time delays of photoemission. More significantly, they have revealed this without the requirement for any experimental time resolution or measurement essentially, without the requirement for a clock. For this, the researchers employed a sort of photoemission spectroscopy to estimate the spin of electrons photo-emitted from a crystal of copper.

“With lasers you can directly estimate the time delay between distinct procedures, but it is intricate to determine when a process starts – time zero,” says Mauro Fanciulli, a Ph. D student of Dil’s group and first author on the paper. “But in our study we estimate time indirectly, so we do not have that issue, we could access one of the smallest timescales ever estimated. The two methods – lasers and spin, are complementary, and together they can yield an entire novel realm of information.”

The information about the timescale of photoemission is comprised in the wave function of the emitted electrons. It is a quantum description of the probability of where any given electron can be identified at a given time. By employing SAPRES, the researchers were able to estimate the spin of the electrons, which in turn enabled them to access their wave function properties