When you flick on a light switch, it feels instant. The bulb goes on, your room brightens, and your brain files the whole thing under \u201czero waiting time.\u201d But at the tiny scales where electrons move, that instant is not really instant at all.<\/p>\n\n\n\n
A new international study led from Ecole Polytechnique F\u00e9d\u00e9rale de Lausanne (EPFL) shows that the time an electron needs to jump to a higher energy state actually depends on the material itself. <\/p>\n\n\n\n
In highly symmetric crystals such as copper, that quantum jump lasts about 26 attoseconds, while in low symmetry, chain-like materials it stretches beyond 200 attoseconds, almost an order of magnitude longer. In other words, there is a kind of \u201cquantum time<\/a>\u201d inside matter, and it runs faster or slower depending on how the atoms are arranged.<\/p>\n\n\n\n The researchers are not proposing a new dimension of time. Here, quantum time is the physical duration of a very simple event at the atomic scale. An electron absorbs a particle of light<\/a>, gains energy, and ends up in a new state.<\/p>\n\n\n\n Energy conservation tells us that such a change cannot be strictly instantaneous. Theory has long suggested that these transitions should last only attoseconds, millionths of a millionth of a millionth of a second, but actually measuring that interval is very hard.<\/p>\n\n\n\n Traditional attosecond experiments use ultrashort laser pulses as a kind of stopwatch. That works, but the \u201cclock\u201d is external to the system and can disturb the very process scientists are trying to time. The new work takes a different route and tries to let the quantum system time itself.<\/p>\n\n\n\n The team built on a concept known as Eisenbud Wigner Smith<\/a> delay, which links time to how the phase of a quantum wave changes during a transition. Instead of watching a stopwatch, they look at how the electron\u2019s wave function twists in energy and space.<\/p>\n\n\n\n Their key trick is to use the electron\u2019s spin as the visible pointer. Spin is an intrinsic quantum property, a bit like a tiny magnetic arrow. When light kicks electrons out of a material, several quantum pathways can lead to the same final state. Those paths interfere with each other, and that interference leaves a clear fingerprint in the spin polarization of the emitted electrons.<\/p>\n\n\n\n By measuring that spin pattern with high precision, the researchers can infer how the phase changes with energy and from there extract a real duration for the transition itself. They describe their measurements as experiments that \u201cdo not require an external clock and provide the timescale needed for the electron wave function to evolve.\u201d <\/p>\n\n\n\n So the timing information does not come from an outside laser pulse. It is encoded inside the quantum process and read out through spin.<\/p>\n\n\n\n Once the method was in place, the obvious question came up. What actually controls this tiny slice of time?<\/p>\n\n\n\n To find out, the team compared materials with different effective dimensionalities, which is a practical way to tune their symmetry. They studied a three-dimensional metal, ordinary copper, two-layered compounds, TiSe\u2082 and TiTe\u2082, and a chain-like material, CuTe.<\/p>\n\n\n\n The pattern was very clear. In three-dimensional copper, the electron transition lasted about 26 attoseconds<\/a>. In the two-layered materials, the process slowed to roughly 140 to 175 attoseconds. In the chain like CuTe, the duration exceeded 200 attoseconds.<\/p>\n\n\n\n Lower symmetry meant longer quantum time. The authors report a direct link between the symmetry of the crystal and the attosecond timescale of the transition itself, not just a relative delay between two different channels. That shifts attention away from only the electronic interaction and toward the underlying geometry of the material.<\/p>\n\n\n\n You can picture it a bit like a crowded subway station. In a perfectly symmetric station with many identical exits, people can spread out and leave quickly. In a narrow corridor with fewer options, everyone slows down. Electrons face a similar situation inside low-symmetry materials.<\/p>\n\n\n\n At first glance, these numbers sound incredibly small. Does it really matter if a process takes 26 or 200 attoseconds? For everyday life right now, probably not. Your light switch and your laptop will work the same tomorrow. But for the most part, modern electronics, solar cells<\/a>, sensors, and even emerging quantum devices rely on how quickly and how cleanly electrons can respond to light or electric fields.<\/p>\n\n\n\n By linking quantum timescales to symmetry, the study offers a new design knob for future materials. Researchers may be able to engineer structures where electrons respond faster for ultrafast detectors, or slower in a controlled way for devices that need built in delays and memory.<\/p>\n\n\n\n The method also gives physicists a rare direct handle on one of the most puzzling questions in quantum theory. Time in quantum mechanics is usually treated as an external parameter, not as something the system itself \u201chas.\u201d <\/p>\n\n\n\n These experiments suggest that, to a large extent, the time of a quantum event emerges from the structure and symmetry of the material where it happens. At the end of the day, that means electrons do not live in a universal, one-size-fits-all instant. Their internal clock depends on the architecture of matter itself.<\/p>\n\n\n\n The study was published in Newton<\/em>, and can be read through the journal\u2019s official page Newton.<\/p>\n","protected":false},"excerpt":{"rendered":" When you flick on a light switch, it feels instant. The bulb goes on, your room brightens, and your brain … <\/p>\nWhat physicists mean by quantum time<\/h2>\n\n\n\n
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Measuring time from inside a quantum jump<\/h2>\n\n\n\n
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How symmetry speeds up or stretches quantum time<\/h2>\n\n\n\n
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Why this matters for future materials and technologies<\/h2>\n\n\n\n