Lifeboat Foundation: Safeguarding Humanity
Toggle light / dark theme

Blog

Category: quantum physics – Page 397

An ultracompact circularly polarized light source is a crucial component for the applications of classical and quantum optics information processing. The development of this field relies on the advances of two fields: quantum materials and chiral optical cavities. Conventional approaches for circularly polarized photoluminescence suffer from incoherent broadband emission, limited DOP, and large radiating angles. Their practical applications are constrained by low efficiency and energy waste to undesired handedness and emission directions. The chiral microlasers can have large DOPs and directional output, but only in specific power ranges. Most importantly, their subthreshold performances plummet significantly. Up to now, the strategy for simultaneous control of chiral spontaneous emission and chiral lasing is still absent.

In a new paper published in Science, researchers from Harbin Institute of Technology and Australian National University employ the physics of chiral quasi in the continuum (BICs) and demonstrate the efficient and controllable emission of circularly polarized light from resonant metasurfaces.

BICs with integer topological charge in momentum space and a theoretically infinite Q factor have been explored for many applications including nonlinear optics and lasing. By introducing in-plane asymmetry, BICs turn to be quasi-BICs with finite but still high Q factors. Interestingly, the integer topological charge of BICs mode would split into two half integer charges, which symmetrically distribute in momentum space and correspond to left-and right-handed circular polarization states, also known as C points.

Read more | >

Over the last decade, improvements in optical atomic clocks have repeatedly led to devices that have broken records for their precision (see Viewpoint: A Boost in Precision for Optical Atomic Clocks). To achieve even better performance, physicists must find a way to cool the atoms in these clocks to lower temperatures, which would allow them to use shallower atom traps and reduce measurement uncertainty. Tackling this challenge, Xiaogang Zhang and colleagues at the National Institute of Standards and Technology, Colorado, have cooled a gas of ytterbium atoms to a record low temperature of a few tens of nanokelvin [1]. As well as enabling the next generation of optical atomic clocks, the researchers say that their technique could be used to cool atoms in neutral-atom quantum computers.

Divalent atoms such as ytterbium are especially suited to precision metrology, as their lack of net electronic spin makes them less sensitive than other species to environmental noise. These atoms can be cooled to the necessary sub-µK temperatures in several ways, but not all techniques are compatible with the requirements of high-precision clocks. For example, evaporative cooling, in which the most energetic atoms are removed, is time-consuming and depletes the atoms. Meanwhile, resolved sideband cooling chills the motion of the atoms only along the axis of the 1D optical trap, leaving their off-axis motion unaffected.

Zhang and colleagues cool their atoms using a laser tuned to ytterbium’s so-called clock transition, whose extremely narrow linewidth means that the atom can theoretically be cooled to below 10 nK. They demonstrate that the precision of a clock employing a shallow lattice trap enabled by such a temperature would not be limited by atoms tunneling between adjacent lattice sites, potentially allowing a measurement uncertainty below 10-19.

Read more | >

For all of history, there’s been an underlying but unspoken assumption about the laws that govern the Universe: If you know enough information about a system, you can predict precisely how that system will behave in the future. The assumption is, in other words, deterministic. The classical equations of motion — Newton’s laws — are completely deterministic. The laws of gravity, both Newton’s and Einstein’s, are deterministic. Even Maxwell’s equations, governing electricity and magnetism, are 100% deterministic as well.

But that picture of the Universe got turned on its head with a series of discoveries that began in the late 1800s. Starting with radioactivity and radioactive decay, humanity slowly uncovered the quantum nature of reality, casting doubt on the idea that we live in a deterministic Universe. Predictively, many aspects of reality could only be discussed in a statistical fashion: where a set of probable outcomes could be presented, but which one would occur, and when, could not be precisely established. The hopes of avoiding the necessity of “quantum spookiness” was championed by many, including Einstein, with the most compelling alternative to determinism put forth by Louis de Broglie and David Bohm. Decades later, Bohmian mechanics was finally put to an experimental test, where it failed spectacularly. Here’s how the best alternative to the spooky nature of reality simply didn’t hold up.

Read more | >

“So a quantum key distribution consists of two things: No. 1, got to have a quantum random number generator, and that’s one of the things that QNu Labs makes,” he said. “The second thing that you need is the receivers in which those two devices connect and be used to convey encrypted messages in this fashion.”

In military use, quantum key distribution would work best in point to point communication — that is, communicating from one person to another. Creating a “true network” that’s able to send the same encrypted message to multiple receivers at once is challenging because the encrypted bit that’s carrying the message eventually begins to lose its coherence and “drops away,” Herman said.

“In the military, where you’re sending extremely sensitive classified data from one office to the next, you want to make sure that no one’s going to be able to break into and decrypt that,” he said. “Well, [quantum key distribution] is definitely a way in which to carry that out.”

Read more | >

This video is episode two from the series “Examining the Big Questions of Time”.
Stream the full series now on Wondrium http://www.Wondrium.com/YouTube.

Just a few decades ago, scientists were absolute in their determination that time began with the Big Bang. But that’s all been turned on its head with the rise of string theory and other fascinating developments in theoretical physics. Learn how those advances brought the pre-Bang universe to the forefront of cosmology.

00:00 Was the Big Bang Really the Beginning of Time?
04:18 Cosmic Microwave Background Radiation.
07:22 Is Relativity Theory Always Valid?
09:06 Origins of String Theory.
13:51 Quantum Strings Introduce Dualities.
17:41 Why Can’t We Perceive All Dimensions of Space?
21:53 New Big Bang Theories and Controversy.
25:37 Observable Consequences of a Pre-Bang Epoch.

Continue reading “The Myth of The Beginning of Time | String Theory and the Big Bang” | >

The popularity of electric vehicles (EVs) as an environmentally friendly alternative to conventional gasoline vehicles has been on the rise. This has led to research efforts directed toward developing high-efficiency EV batteries. But, a major inefficiency in EVs results from inaccurate estimations of the battery charge. The charge state of an EV battery is measured based on the current output of the battery. This provides an estimate of the remaining driving range of the vehicles.

Typically, the currents in EVs can reach hundreds of amperes. However, commercial sensors that can detect such currents cannot measure small changes in the at milliampere levels. This leads to an ambiguity of around 10% in the battery charge estimation. What this means is that the driving range of EVs could be extended by 10%. This, in turn, would reduce inefficient battery usage.

Now, a team of researchers from Japan, led by Professor Mutsuko Hatano from Tokyo Institute of Technology (Tokyo Tech), has now come up with a solution. In their study published in Scientific Reports, the team has reported a diamond quantum sensor-based detection technique that can estimate the battery charge within 1% accuracy while measuring high currents typical of EVs.

Read more | >