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JILA physicists have boosted the signal power of their atomic “tweezer clock” and measured its performance in part for the first time, demonstrating high stability close to the best of the latest generation of atomic clocks.

The unusual clock, which uses laser tweezers to trap, control and isolate atoms, offers unique possibilities for enhancing clock performance using the tricks of quantum physics as well as future applications in quantum information processing, quantum simulation, and measurement science.

Described in a Nature paper published online Dec. 16, the clock platform is a rectangular grid of about 150 strontium atoms confined individually by optical tweezers, which are created by a laser beam aimed through a microscope and deflected into 320 spots. This upgraded version of the clock has up to 30 times as many atoms as the preliminary design unveiled last year, due mainly to the use of several different lasers, including a green one for trapping the atoms and two red ones to make them “tick.”

A joint team of researchers at Fermilab and partner institutions have achieved quantum teleportation, teleporting information over a distance of 44 kilometers. The remarkable achievement supports the premise that scientists and engineers can build a workable and high-fidelity quantum network using practical devices.

A new study illuminates surprising choreography among spinning atoms. In a paper appearing in the journal Nature, researchers from MIT and Harvard University reveal how magnetic forces at the quantum, atomic scale affect how atoms orient their spins.

In experiments with ultracold lithium atoms, the researchers observed different ways in which the spins of the atoms evolve. Like tippy ballerinas pirouetting back to upright positions, the spinning atoms return to an equilibrium orientation in a way that depends on the magnetic forces between individual atoms. For example, the atoms can spin into equilibrium in an extremely fast, “ballistic” fashion or in a slower, more diffuse pattern.

The researchers found that these behaviors, which had not been observed until now, could be described mathematically by the Heisenberg model, a set of equations commonly used to predict magnetic behavior. Their results address the fundamental nature of magnetism, revealing a diversity of behavior in one of the simplest magnetic materials.

More than two-thirds of the energy used worldwide is ultimately ejected as “waste heat.” Within that reservoir of discarded energy lies a great and largely untapped opportunity, claim scientists in MIT’s Department of Nuclear Science and Engineering (NSE). As reported in a recent issue of Nature Communications, the MIT team—led by Assistant Professor Mingda Li, who heads NSE’s Quantum Matter Group—has achieved a breakthrough in thermoelectric generation, which offers a direct means of converting thermal energy, including waste heat, into electricity.

A temperature gradient, or difference, within a material such as a metal or semiconductor can, through a phenomenon known as the Seebeck effect, give rise to an electrical voltage that drives a current. “For many materials, the thermoelectric effect is too low to be useful,” explains NSE Research Scientist Fei Han. “Our goal is to find materials with conversion efficiencies high enough to make thermoelectric generation more practical.”

The efficiency of thermoelectric energy conversion is proportional to a material’s temperature, electrical conductivity, and something called the “thermopower” squared; it is inversely proportional to the thermal conductivity. Because efficiency goes up with temperature, most thermoelectric materials used today operate in the range of hundreds of degrees centigrade. “But in our lives, most of the stuff around us is at room temperature,” Han says. “That’s why we’re trying to discover new materials that work effectively at or below room temperature.”

Since the very beginning of quantum physics, a hundred years ago, it has been known that all particles in the universe fall into two categories: fermions and bosons. For instance, the protons found in atomic nuclei are fermions, while bosons include photons — which are particles of light — as well as the BroutEnglert-Higgs boson, for which Francois Englert, a professor at ULB, was awarded a Nobel Prize in Physics in 2013.

Bosons — especially photons — have a natural tendency to clump together. One of the most remarkable experiments that demonstrated photons’ tendency to coalesce was conducted in 1987, when three physicists identified an effect that was since named after them: the Hong-Ou-Mandel effect. If two photons are sent simultaneously, each towards a different side of a beam splitter — a sort of semitransparent mirror — one could expect that each photon will be either reflected or transmitted.

Logically, photons should sometimes be detected on opposite sides of this mirror, which would happen if both are reflected or if both are transmitted. However, the experiment has shown that this never actually happens: the two photons always end up on the same side of the mirror, as though they ‘preferred’ sticking together! In an article published recently in US journal Proceedings of the National Academy of Sciences, Nicolas Cerf — a professor at the Centre for Quantum Information and Communication (École polytechnique de Bruxelles) — and his former PhD student Michael Jabbour — now a postdoctoral researcher at the University of Cambridge — describe how they identified another way in which photons manifest their tendency to stay together. Instead of a semi-transparent mirror, the researchers used an optical amplifier, called an active component because it produces new photons.

Collaboration achieves sustained high-fidelity quantum teleportation over a distance of 44 kilometers.

For the first time, physicists measured fluctuations in the quantum realm.

New technique could be useful for quantum information processing.

A new technique to cool reactive molecules to temperatures low enough to achieve quantum degeneracy – something not generally possible before – has been created by researchers in the US. In this temperature regime, the dominance of quantum effects over thermal fluctuations should allow researchers to study new quantum properties of molecules. As a first example, the researchers demonstrated how a slight change in applied electric field can alter the reaction rate between molecules by three orders of magnitude. The researchers hope their platform will enable further exploration of molecular quantum degeneracy, with potential applications ranging from quantum many body physics to quantum information processing.

When atoms are cooled close to absolute zero, the blur created by thermal effects that govern their behaviour in the classical world around us is removed, making their quantum nature clear. This has led to some fascinating discoveries. In ultracold quantum bosonic or fermion-pair quantum gases, for example, all the atoms in a trap can simultaneously occupy the quantum ground state, resulting in a wavefunction that is macroscopic.

Continue reading “Physicists fine tune chemical reaction rates for ultracold molecules” »

Specialists from the University of Copenhagen created a chip that could be used to build a future quantum simulator.