Nanowerk February 28, 2022 The boomerang effect is a disorder-induced behavior which inhibits transport of electrons turning what would otherwise be a conducting material into an insulator. An international team of researchers (USA – UC Santa Barbara, Brazil, France) reported experimental observation and characterization of this surprising quantum-mechanical phenomenon. They exposed a gas of ultracold lithium atoms to a phase-shifted pair of optical lattices to realize a “quantum kicked rotor,” a momentum-space realization of Anderson-localized matter. They observed the characteristic departure from and return to the origin that is the key signature of the boomerang effect. Detailed characterization revealed the […]
Category Archives: Quantum science
Physicists harness electrons to make ‘synthetic dimensions’
Phys.org February 21, 2022 To push spatial boundaries researchers at Rice University developed a technique to engineer the Rydberg states of ultracold strontium atoms by applying resonant microwave electric fields to couple many states together, making the levels look like particles that just move around between locations in space. Rydberg atoms possess many regularly spaced quantum energy levels, which can be coupled by microwaves that allow the highly excited electron to move from level to level. They demonstrated their techniques by making a 1D lattice using lasers to cool strontium atoms and applied microwaves with alternating weak and strong couplings […]
Quantum marbles in a bowl of light
Science Daily December 22, 2021 Quantum mechanics sets fundamental limits on how fast quantum states can be transformed in time. Two well-known quantum speed limits are the Mandelstam-Tamm and the Margolus-Levitin bounds, which relate the maximum speed of evolution to the system’s energy uncertainty and mean energy, respectively. An international team of researchers (Israel, Germany) tested concurrently both limits in a multilevel system by following the motion of a single atom in an optical trap using fast matter wave interferometry. They found two different regimes: one where the Mandelstam-Tamm limit constrains the evolution at all times. But there was also […]
‘Crazy’ light emitters: Physicists see an unusual quantum phenomenon
Nanowerk December 14, 2021 An international team of researchers (Germany, USA – Lawrence Berkeley National Laboratory, Sweden, Japan) has visualized the rapid movement of excitons in atomically thin semiconductors using highly sensitive optical microscopy. First, they applied a short laser pulse to the material and then used an ultrafast detector to observe when and where the light was reemitted. They found the excitons to move in opposite directions at the same time. The only possible explanation was that the excitons would occasionally move through closed loops in opposite directions at the same time. Such behavior was in fact known from […]
Evading the uncertainty principle in quantum physics
Phys.org May 6, 2021 Quantum mechanics sets a limit for the precision of continuous measurement of the position of an oscillator. An international team of researchers (Finland, Australia) has developed a theoretical model to show that there is a way to get around the uncertainty principle. In their experiment they used two vibrating drumheads vibrating in opposite phase to each other cancelling the quantum uncertainty of the drums’ motion if the two drums are treated as one quantum-mechanical entity. Thus the researchers were able to simultaneously measure the position and the momentum of the two drumheads – which should not […]
A speed limit also applies in the quantum world
Science Daily February 19, 2021 In two-level systems, the quantum brachistochrone solutions are long known but they are not applicable to larger systems, especially when the target state cannot be reached through a local transformation. An international team of researchers (Germany, USA – MIT, Italy) has demonstrated fast coherent transport of an atomic wave packet over 15 times its size, a case of quantum processes going beyond the two-level system. The measurements of the transport fidelity revealed the existence of a minimum duration—a quantum speed limit—for the coherent splitting and recombination of matter waves. They obtained physical insight into this […]
Quantum Theory May Twist Cause And Effect Into Loops, With Effect Causing The Cause
Science Alert February 14, 2021 Quantum correlations violating Bell inequalities defy satisfactory causal explanations within the framework of classical causal models. The first challenge has been addressed through the recent development of intrinsically quantum causal models, allowing causal explanations of quantum processes – provided they admit a definite causal order, i.e., have an acyclic causal structure. An international team of researchers addresses causally nonseparable processes and offers a causal perspective on them through extending quantum causal models to cyclic causal structures. Among other applications of the approach, it is shown that all unitarily extendible bipartite processes are causally separable and […]
Adding or subtracting single quanta of sound
Science Daily January 25, 2021 An international team of researchers (UK, Denmark, Australia) injected laser light into a crystalline microresonator that supports both the light and the high-frequency sound waves. The two types of waves coupled to one another via an electromagnetic interaction creates light at a new frequency. To subtract a single phonon, the team detected a single photon that has been up shifted in frequency. Detecting a single photon indicates that a subtracted single phonon. When the experiment is performed at a finite temperature, the sound field has random fluctuations from thermal noise. Counterintuitively, when you subtract a […]
Mapping quantum structures with light to unlock their capabilities
Nanowerk December 4, 2020 All-optical band-structure reconstruction could directly connect electronic structure with the coveted quantum phenomena if strong light waves transported localized electrons within preselected bands. An international team of researchers (USA – University of Michigan, Germany) has shown that harmonic sideband (HSB) generation in monolayer tungsten diselenide creates distinct electronic interference combs in momentum space. Locating these momentum combs in spectroscopy enables super-resolution tomography of key band-structure details in situ. They experimentally tuned the optical-driver frequency by a full octave and showed that the predicted super-resolution manifests in a critical intensity and frequency dependence of HSBs. The concept […]
Demonstrating entanglement through a fiber cable with high fidelity
Phys.org August 13, 2020 Researchers in the UK exploited a property of quantum physics that allows for mapping the medium (fiber cable) onto the quantum state of a particle moving through it to transport entangled particles through a commercial fiber cable with 84.4% fidelity. They sent one of a pair of photons through a complex medium, but not the other. Both were then directed toward spatial light modulators and then on to detectors, and then finally to a device used to correlate coincidence counting. In their setup, light from the photon that did not pass through the complex medium propagated […]