Time Measurement Methods in Quantum Systems

An entirely new way to measure time has been discovered thanks to quantum physicists studying strange patterns inside atoms. In a recent study from Uppsala University, researchers found a method of telling time that doesn’t rely on a ticking clock or a clear starting point. Instead, it uses the natural patterns created by energized atoms, specifically, helium atoms pumped into extreme energy states known as Rydberg states. These atoms behave very differently at the quantum level, where electrons don’t move in predictable paths but follow odd, wave-like behavior. When electrons are nudged into these Rydberg states with lasers, their movements form patterns known as Rydberg wave packets. These wave packets can interfere with one another, like ripples crossing in a pond, creating complex patterns that change over time. It turns out that these interference patterns act like fingerprints, and each one matches a specific moment in time. What makes this remarkable is that you don’t need a clear “start” to track how much time has passed. Instead, you can look at the pattern itself and identify exactly where in time you are, kind of like being able to tell how far into a song you are just by hearing a few notes. In their experiment, the scientists hit helium atoms with laser pulses and then read the resulting interference pattern. They found that these patterns reliably matched up with theoretical predictions, proving they could be used as precise timestamps. This is especially useful in quantum experiments, where it’s hard to define a clear “now” or “then,” and even harder to measure events that last just trillionths of a second. Source: Berholts, Marta, et al. "Quantum watch and its intrinsic proof of accuracy." Physical Review Research 4.4 (2022): 043041.

Quantum Time Isn’t Instant: Physicists Measure the True Duration of Ultrafast Events Introduction At everyday scales, time appears smooth and continuous. But at the quantum level, events unfold in fleeting intervals that challenge classical intuition. Physicists have now developed a method to directly measure how long ultrafast quantum transitions last—without relying on an external clock—revealing that these processes are not instantaneous and are shaped by atomic structure. The Breakthrough Measurement • Researchers tracked electrons as they absorbed light and escaped from a material. • Instead of using a separate timing reference, they inferred duration from subtle changes in the electron’s behavior during emission. • This approach allowed them to extract intrinsic time scales directly from the quantum system itself. What They Found • Quantum transitions take a measurable amount of time—they are not instantaneous jumps. • The duration of these events depends strongly on the atomic structure of the material. • Different materials produce different escape dynamics for electrons, effectively altering “quantum time” at ultrafast scales. Why Atomic Structure Matters • The arrangement of atoms influences how electrons interact with surrounding fields. • These interactions modify how energy is absorbed and how electrons transition between states. • As a result, the microscopic architecture of a material can speed up or slow down quantum processes. Why This Matters Understanding the true duration of quantum events reshapes how scientists think about time in quantum mechanics. It has implications for ultrafast spectroscopy, next-generation electronics, and quantum technologies where control over electron motion is critical. By demonstrating that quantum transitions have structure-dependent timing, this work moves beyond abstract theory and into measurable reality. It shows that even at nature’s fastest scales, time is not just a backdrop—it is an emergent property shaped by the physical system itself.

Researchers have recorded the briefest interval of time ever measured: 247 zeptoseconds—the duration for a photon of light to traverse a hydrogen molecule. That's 0.000000000000000000247 seconds. A zeptosecond equals one trillionth of a billionth of a second, a realm where light, the universe's speed champion, advances mere fractions of an atomic diameter. For scale, a single second contains as many zeptoseconds as there are seconds in 31.7 trillion years—vastly exceeding the age of the cosmos. Physicist Reinhard Dörner and colleagues at Goethe University Frankfurt achieved this using intense X-rays from Hamburg's PETRA III accelerator. They aimed at hydrogen molecules—the simplest in existence, comprising two protons and two electrons. An incoming photon struck both electrons in rapid sequence, akin to a stone skipping across water. To resolve this fleeting event, the team employed a COLTRIMS reaction microscope, an ultra-precise instrument that tracks particle positions and momenta. By examining the interference patterns from the two expelled electrons, they pinpointed the precise lag between the photon's impact on the first electron and the second.The finding: 247 zeptoseconds. This demonstrates that light does not illuminate a molecule instantaneously, even at this tiny scale; the delay stems from light's finite velocity of roughly 186,000 miles per second (300,000 km/s). It represents the first direct observation of light propagating inside a molecule. By contrast, chemical reactions unfold over femtoseconds—a thousandfold longer. Zeptosecond precision opens a window into quantum timescales, where electron and photon dynamics govern matter's core behaviors. https://lnkd.in/g4R_x7wA

Hey You! Got a quick Attosecond? For decades, we’ve talked about quantum entanglement as if it “just happens.” Now we’re starting to put a clock on how it forms. A team led by TU Wien (Vienna University of Technology), working with collaborators in China, used ultrafast simulations and a proposed two-laser measurement protocol to resolve the temporal structure of an event that’s usually treated as instantaneous. The mind-bender is that the departing electron doesn’t have a single, well-defined “birth time.” Instead, that timing is quantum-linked to the energy state of the electron left behind—with an average offset on the order of ~232 attoseconds. That’s 0.000000000000000232 seconds. To give you some perspective - a blink of an eye (~0.1 seconds) is about 430 trillion times longer than 232 attoseconds Here’s the physical picture they analyze: Start with an atom that has two electrons. Hit it with an extremely intense, high-frequency laser pulse. One electron is ripped out (ionized) and rushes away. The second electron remains bound, but can be kicked into a different (higher-energy) state. At that point, the system is no longer well-described as “electron A plus electron B.” The key outcome is that the two electrons become one joint quantum object—their properties are correlated in a way that can’t be reduced to independent “facts” about each electron. The most interesting twist is what becomes entangled. In their analysis, the “birth time” of the escaping electron—the moment it truly “left” the atom—is not a single, definite timestamp. Instead, it’s in a quantum superposition of different departure times, and those possible times are linked to the energy state of the electron left behind. Practically, that means: If the remaining electron ends up in a higher-energy state, the departing electron was more likely ejected earlier. If the remaining electron ends up in a lower-energy state, the departing electron was more likely ejected later—with an average offset on the order of ~232 attoseconds (232 × 10⁻¹⁸ seconds). That’s the real substance behind the popular phrasing “entanglement speed.” The point is not that entanglement is slow—it’s that even “instantaneous” quantum events can have measurable internal timing when you probe them on attosecond scales. Why it matters (beyond the headline): If you can resolve when and how correlations form—rather than only confirming they exist after the fact—you get leverage. You move from “entanglement is a weird thing we observe” to “entanglement is a dynamical process we can potentially engineer, shape, and control.” https://lnkd.in/gqPn34FA #QuantumEntanglement #QuantumPhysics #Attosecond #UltrafastScience #LaserPhysics #ElectronDynamics #AtomicPhysics #QuantumInformation #QuantumResearch #Physics

GEOMETRY OF MATTER CONTROLS THE QUANTUM TIMESCALE The longstanding question of how long a quantum transition actually takes has moved to experimentally accessible physics. In the attosecond regime, the transition from an initial bound state to a final photoelectron state is governed not by an external clock but by the internal phase evolution of the electronic wavefunction. The EPFL study demonstrates that this timescale is not universal: it is a symmetry‑dependent property of the material’s electronic structure. The key advance is the use of spin‑ and angle‑resolved photoemission (SARPES) to extract the EWS delay directly from the spin texture of the emitted electrons. In systems with strong spin–orbit coupling, multiple partial waves contribute to the photoemission amplitude. Their interference generates a measurable spin polarization even in nonmagnetic crystals under linearly polarized excitation. Because the spin vector is locked to the relative phase between these channels, it becomes an intrinsic probe of the accumulated phase—and therefore of the transition time—without perturbing the system with an external streaking field. Applying this method across materials of different dimensionality reveals a robust inverse relationship between spatial symmetry and quantum transition time. In 3D Cu with high cubic symmetry, the EWS delay approaches the lower theoretical bound (~26 as). In quasi‑2D TiSe₂ and TiTe₂, the delay increases to ~150 as, independent of correlation strength. This monotonic increase cannot be attributed to electron–electron interactions; instead, it reflects the reduction in the number of symmetry‑allowed propagation channels. The physical picture is that the excited electron occupies a quasi‑stationary state whose lifetime is determined by the density and symmetry of available decay pathways. High‑symmetry 3D lattices support many equivalent channels for constructive interference, enabling rapid phase accumulation and fast emission. As dimensionality is reduced, the Hilbert space of allowed momenta contracts, forcing the electron to undergo a more complex internal phase evolution before escape. The result is a geometry‑induced temporal bottleneck. These findings have several implications for condensed‑matter physics. First, they establish time as a symmetry‑controlled material parameter, not a universal constant of the photoemission process. Second, they impose fundamental constraints on petahertz‑scale electronics, where low‑dimensional nanostructures—despite their technological appeal—will exhibit intrinsically longer response times. Third, the spin‑interference method provides a new route to attosecond‑scale dynamics in systems where strong external fields would destroy fragile quantum phases, including correlated materials and topological states. The results show that spatial symmetry and temporal evolution are deeply entangled. In quantum materials, the structure of space dictates the flow of time.

⌛ How do you measure large quantum superpositions of time? ⌛ Measuring a time-bin qubit (d=2) normally requires an unbalanced (Franson) interferometer that coherently combines an early and late time-bin. Extending this to high-dimensional (d>2) time-bin quDits is very difficult, usually requiring multiple, bulky, phase-stabilized interferometers that are difficult to align. We show how a high-dimensional time-bin quDit (d=11) can be measured by harnessing space-time coupling in a multi-mode fiber. We use wavefront shaping in space to program large, multi-mode unbalanced (Franson) interferometers for time **inside** the fiber! (Paper link in comments) Very happy to see my idea from 7 years ago come to life, with incredible work by my group members Dylan Danese, Vatshal Srivastav, Saroch Leedumrongwatthanakun, and Will McCutcheon!