beecee Posted March 19, 2019 Posted March 19, 2019 https://cosmosmagazine.com/physics/quantum-tunnelling-is-instantaneous-researchers-find Quantum tunnelling is instantaneous, researchers find: Researchers have found that electrons passing through solid matter in a quantum process known as “tunnelling” do so instantaneously. The finding, led by scientists from Australia’s Griffith University, contradicts previous experiments that suggested a degree of time elapses between the start and finish of a tunnelling event. The work is detailed in a paper in the journal Nature. Quantum tunnelling is one of the more bizarre differences between our everyday, classical world and the surprising realm of quantum mechanics. “If you lean on a wall, that wall pushes back in force so that you don’t go through it,” co-author Robert Sang says. “But when you go down to the microscopic level, things behave quite differently. This is where the laws of physics change from classical to quantum.” more at https://cosmosmagazine.com/physics/quantum-tunnelling-is-instantaneous-researchers-find extract: “It came out to agree with the theory within experimental uncertainty being consistent with instantaneous tunnelling.” The precision of the clock to measure the tunnelling event was driven by the ultra-fast pulse of light in the attosecond laser – just a billionth of a billionth of a second long. The energy emitted by the laser during such a tiny amount of time is greater than that of the entire US power grid." the paper: https://www.nature.com/articles/s41586-019-1028-3 Attosecond angular streaking and tunnelling time in atomic hydrogen: Abstract The tunnelling of a particle through a potential barrier is a key feature of quantum mechanics that goes to the core of wave–particle duality. The phenomenon has no counterpart in classical physics, and there are no well constructed dynamical observables that could be used to determine ‘tunnelling times’. The resulting debate1,2,3,4,5 about whether a tunnelling quantum particle spends a finite and measurable time under a potential barrier was reignited in recent years by the advent of ultrafast lasers and attosecond metrology6. Particularly important is the attosecond angular streaking (‘attoclock’) technique7, which can time the release of electrons in strong-field ionization with a precision of a few attoseconds. Initial measurements7,8,9,10 confirmed the prevailing view that tunnelling is instantaneous, but later studies11,12 involving multi-electron atoms—which cannot be accurately modelled, complicating interpretation of the ionization dynamics—claimed evidence for finite tunnelling times. By contrast, the simplicity of the hydrogen atom enables precise experimental measurements and calculations13,14,15and makes it a convenient benchmark. Here we report attoclock and momentum-space imaging16 experiments on atomic hydrogen and compare these results with accurate simulations based on the three-dimensional time-dependent Schrödinger equation and our experimental laser pulse parameters. We find excellent agreement between measured and simulated data, confirming the conclusions of an earlier theoretical study17 of the attoclock technique in atomic hydrogen that presented a compelling argument for instantaneous tunnelling. In addition, we identify the Coulomb potential as the sole cause of the measured angle between the directions of electron emission and peak electric field: this angle had been attributed11,12 to finite tunnelling times. We put an upper limit of 1.8 attoseconds on any tunnelling delay, in agreement with recent theoretical findings18 and ruling out the interpretation of all commonly used ‘tunnelling times’19as ‘time spent by an electron under the potential barrier’20.
swansont Posted March 20, 2019 Posted March 20, 2019 13 hours ago, beecee said: The energy emitted by the laser during such a tiny amount of time is greater than that of the entire US power grid. One has to wonder about the quality of a summary that makes such a fundamental error, mistaking power and energy. 1
beecee Posted March 20, 2019 Author Posted March 20, 2019 8 hours ago, swansont said: One has to wonder about the quality of a summary that makes such a fundamental error, mistaking power and energy. Thanks for that pick-up. I suppose it highlights the fact that even science writers [as distinct from scientists] are prone to sensationalism in journalism at times.
swansont Posted March 21, 2019 Posted March 21, 2019 The effect here is similar to the experiments where a light pulse seems to exit a region before it enters it — it's some sleight-of-hand with looking at a pulse, and playing around with how that pulse (since it has a width) corresponds to location. "No, Quantum Tunneling Didn't Break The Speed Of Light; Nothing Does" Quote You might think, based on what you just read about the speed of quantum tunneling being instantaneous, that this means that particles can travel infinitely fast, breaking the speed of light, through a quantum mechanical barrier of finite, non-zero thickness. That's the misinterpretation that always crops up, and how people fool themselves (and unscrupulous news organizations try to fool you) into thinking they're breaking the speed of light. https://www.forbes.com/sites/startswithabang/2019/03/21/no-quantum-tunneling-didnt-break-the-speed-of-light-nothing-does/#5cda20b77c3c 1
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