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A time crystal, as originally proposed in 2012, is a new state of matter in which the particles are in continuous oscillatory motion. Time crystals break time-translation symmetry. Discrete time crystals do so by oscillating under the influence of a periodic external parametric force, and this type of time crystal has been demonstrated in trapped ions, atoms and spin systems.

Continuous time crystals are more interesting and arguably more important, as they exhibit continuous time-translation symmetry but can spontaneously enter a regime of periodic motion, induced by a vanishingly small perturbation. It is now understood that this state is only possible in an open system, and a continuous quantum-time-crystal state has recently been observed in a quantum system of ultracold atoms inside an optical cavity illuminated with light.

In a paper published in Nature Physics, researchers at University of Southampton in the U.K. showed that a classical metamaterial nanostructure can be driven to a state that exhibits the same key characteristics of a continuous time crystal.

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The motion of an electron in a strong infrared laser field is tracked in real time by means of a novel method developed by MPIK physicists and applied to confirm quantum-dynamics theory by cooperating researchers at MPI-PKS. The experimental approach links the absorption spectrum of the ionizing extreme ultraviolet pulse to the free-electron motion driven by the subsequent near-infrared pulse. Their paper is published in the journal Physical Review Letters.

For this experimental scheme, the classical description of the electron motion is justified even though it is a quantum object. In the future, the new method demonstrated here for helium can be applied to more complex systems such as larger atoms or molecules for a broad range of intensities.

Continue reading “Electron re-collision tracked in real time” »

A new low-temperature growth and fabrication technology allows the integration of 2D materials directly onto a silicon circuit, which could lead to denser and more powerful chips.

Researchers from MIT

MIT is an acronym for the Massachusetts Institute of Technology. It is a prestigious private research university in Cambridge, Massachusetts that was founded in 1861. It is organized into five Schools: architecture and planning; engineering; humanities, arts, and social sciences; management; and science. MIT’s impact includes many scientific breakthroughs and technological advances. Their stated goal is to make a better world through education, research, and innovation.

A new kind of 3D optical lattice traps atoms using focused laser spots replicated in multiple planes and could eventually serve as a quantum computing platform.

Researchers have produced 3D lattices of trapped atoms for possible quantum computing tasks, but the standard technology doesn’t allow much control over atom spacing. Now a team has created a new type of 3D lattice by combining optical tweezers—points of focused light that trap atoms—with an optical phenomenon known as the Talbot effect [1]. The team’s 3D tweezer lattice has sites for 10,000 atoms, but with some straightforward modifications, the system could reach 100,000 atoms. Such a large atom arrangement could eventually serve as a platform for a quantum computer with error correction.

3D optical lattices have been around for decades. The standard method for creating them involves crossing six laser beams to generate a 3D interference pattern that traps atoms in either the high-or low-intensity spots (see Synopsis: Pinpointing Qubits in a 3D Lattice). These cold-atom systems have been used as precision clocks and as models of condensed-matter systems. However, the spacing between atoms is fixed by the wavelength of the light, which can limit the control researchers have over the atomic behavior.

Twenty years ago, Ferenc Krausz, Theodor Hänsch, and their collaborators used a femtosecond near-infrared (NIR) laser to compel neon atoms to emit pulses of extreme ultraviolet (XUV) light that lasted a few hundred attoseconds. The landmark feat depended on the laser’s strong oscillating electric field, which tore away the atoms’ valence electrons and hurled them back half a cycle later. Now Tobias Heldt of the Max Planck Institute for Nuclear Physics in Germany and his collaborators have developed a new experimental technique that is, in a sense, a mirror image of the 2003 demonstration: they used attosecond XUV pulses to free the valence electrons and to then track their response to femtosecond NIR laser pulses [1].

When a few-cycle femtosecond NIR pulse passes through helium gas, the atoms’ dipole moments fluctuate as the electrons move away and then recollide. Those fluctuations in turn are manifest in the gas’s absorption spectrum. Heldt and his collaborators set out to measure the fluctuations and, from them, infer the electrons’ trajectories.

The attosecond XUV pulse in their experiment did double duty. It ionized the helium atoms to bring the electrons under the influence of the NIR pulse. It also interfered with the fluctuating dipole moments. As a result, the XUV pulse carried away the dipoles’ spectral imprint, which the team measured with a grating spectrometer.

A proposed technique would use light and nanowires to generate electron beams with nearly pure spin polarization.

In a polarized electron beam, the particles’ spins are not randomly oriented but favor a particular direction. The polarization serves as a useful property for studying the magnetism of materials or for probing the spins of atoms or nuclei. But such a beam typically has a low degree of polarization unless it is produced at a synchrotron facility. Theorists have proposed creating these beams using laser light, but so far these approaches have involved extremely intense lasers and have not been expected to produce high polarization. Now Deng Pan of East China Normal University and Hongxing Xu of Wuhan University, China, have proposed a method that reduces the required laser intensity by up to 10 billion times compared with previous laser-based approaches and that should produce a pair of beams that are nearly 100% polarized [1].

In Pan and Xu’s proposal, a wide laser beam broadsides an array of parallel conducting nanowires with 100-nm spacing and excites them to emit electromagnetic waves. An unpolarized electron beam is sent across the array, perpendicular to the wires, about 100 nm away from them. Some electrons absorb or emit photons, causing their spins to align parallel or antiparallel to the local electric field. They also gain or lose a photon’s worth of energy. This interaction with the radiation near the wires generates two new beams with nearly pure spin polarizations and slightly different energies, allowing them to be easily separated. Pan and Xu say that the technique should be implementable with current technology and that it may even lead to new ways of manipulating electrons.

For the first time, researchers have demonstrated a prototype lidar system that uses quantum detection technology to acquire 3D images while submerged underwater. The high sensitivity of this system could allow it to capture detailed information even in extremely low-light conditions found underwater.

“This technology could be useful for a wide range of applications,” said research team member Aurora Maccarone, a Royal Academy of Engineering research fellow from Heriot-Watt University in the United Kingdom. “For example, it could be used to inspect underwater installations, such as underwater wind farm cables and the submerged structure of the turbines. Underwater lidar can also be used for monitoring or surveying submerged archaeology sites and for security and defense applications.”

Continue reading “Quantum lidar prototype acquires real-time 3D images while fully submerged underwater” »

The state of perfect stillness known as absolute zero is one of the Universe’s impossible achievements. As close as we can get, the laws of physics will always prevent us from hitting thermal rock bottom.

An international team of researchers has now identified a new theoretical route to reach the mythical mark of zero Kelvin, or-273.15 degrees Celsius (−459.67 degrees Fahrenheit). No, it’s not more likely to break any laws and remove every last shimmer of heat, but the framework could inspire new ways of exploring matter at low temperatures.

As a consequence of the third law of thermodynamics, the removal of increments of heat energy from a group of particles to cool them to absolute zero will always take an infinite number of steps. As such, it requires an infinite amount of energy to achieve. Quite the challenge.

Inside the proton are elementary particles called quarks. Quarks and protons have an intrinsic angular momentum called spin. Spin can point in different directions. When it is perpendicular to the proton’s momentum, it is called a transverse spin. Just like the proton carries an electric charge, it also has another fundamental charge called the tensor charge. The tensor charge is the net transverse spin of quarks in a proton with transverse spin.

The only way to obtain the tensor charge from experimental data is using the theory of quantum chromodynamics (QCD) to extract the “transversity” function. This universal function encodes the difference between the number of quarks with their spin aligned and anti-aligned to the proton’s spin when it is in a transverse direction. Using state-of-the-art data science techniques, researchers recently made the most precise empirical determination of the tensor charge.

Due to the phenomenon known as confinement, quarks are always bound in the proton or other hadrons (particles with multiple quarks). The challenge is to connect the theory of quark interactions (QCD) to experimental measurements of high-energy collisions involving hadrons.