Tyler O'Neal, Staff Editor VISUALIZATION

NIST team directs, measures quantum drum duet

Like conductors of a spooky symphony, researchers at the National Institute of Standards and Technology (NIST) have "entangled" two small mechanical drums and precisely measured their linked quantum properties. Entangled pairs like this might someday perform computations and transmit data in large-scale quantum networks.

The NIST team used microwave pulses to entice the two tiny aluminum drums into a quantum version of the Lindy Hop, with one partner bopping in a cool and calm pattern while the other was jiggling a bit more. Researchers analyzed radar-like signals to verify that the two drums' steps formed an entangled pattern -- a duet that would be impossible in the everyday classical world.

What's new is not so much the dance itself but the researchers' ability to measure the drumbeats, rising and falling by just one quadrillionth of a meter, and verify their fragile entanglement by detecting subtle statistical relationships between their motions.

The research is described in the May 7 issue of Science. researchers entangled the beats of these two mechanical drums--tiny aluminum membranes each made of about 1 trillion atoms--and precisely measured their linked quantum properties. Entangled pairs like this (shown in this colorized micrograph), which are massive by quantum standards, might someday perform computations and transmit data in large-scale quantum networks. CREDIT Teufel/NIST

"If you analyze the position and momentum data for the two drums independently, they each simply look hot," NIST physicist John Teufel said. "But looking at them together, we can see that what looks like random motion of one drum is highly correlated with the other, in a way that is only possible through quantum entanglement."

Quantum mechanics was originally conceived as the rulebook for light and matter at atomic scales. However, in recent years researchers have shown that the same rules can apply to increasingly larger objects such as the drums. Their back-and-forth motion makes them a type of system known as a mechanical oscillator. Such systems were entangled for the first time at NIST about a decade ago, and in that case, the mechanical elements were single atoms.

Since then, Teufel's research group has been demonstrating quantum control of drumlike aluminum membranes suspended above sapphire mats. By quantum standards, the NIST drums are massive, 20 micrometers wide by 14 micrometers long and 100 nanometers thick. They each weigh about 70 picograms, which corresponds to about 1 trillion atoms.

Entangling massive objects is difficult because they interact strongly with the environment, which can destroy delicate quantum states. Teufel's group developed new methods to control and measure the motion of two drums simultaneously. The researchers adapted a technique first demonstrated in 2011 for cooling a single drum by switching from steady to pulsed microwave signals to separately optimize the steps of cooling, entangling, and measuring the states. To rigorously analyze the entanglement, experimentalists also worked more closely with theorists, an increasingly important alliance in the global effort to build quantum networks.

The NIST drum set is connected to an electrical circuit and encased in a cryogenically chilled cavity. When a microwave pulse is applied, the electrical system interacts with and controls the activities of the drums, which can sustain quantum states like entanglement for approximately a millisecond, a long time in the quantum world.

For the experiments, researchers applied two simultaneous microwave pulses to cool the drums, two more simultaneous pulses to entangle the drums, and two final pulses to amplify and record the signals representing the quantum states of the two drums. The states are encoded in a reflected microwave field, similar to radar. Researchers compared the reflections to the original microwave pulse to determine the position and momentum of each drum.

To cool the drums, researchers applied pulses at a frequency below the cavity's natural vibrations. As in the 2011 experiment, the drumbeats converted applied photons to the cavity's higher frequency. These photons leaked out of the cavity as it filled up. Each departing photon took with it one mechanical unit of energy -- one phonon, or one quantum -- from drum motion. This got rid of most of the heat-related drum motion.

To create entanglement, researchers applied microwave pulses in between the frequencies of the two drums, higher than drum 1 and lower than drum 2. These pulses entangled drum 1 phonons with the cavity's photons, generating correlated photon-phonon pairs. The pulses also cooled drum 2 further, as photons leaving the cavity were replaced with phonons. What was left was mostly pairs of entangled phonons shared between the two drums.

To entangle the phonon pairs, the duration of the pulses was crucial. Researchers discovered that these microwave pulses needed to last longer than 4 microseconds, ideally 16.8 microseconds, to strongly entangle the phonons. During this time period, the entanglement became stronger and the motion of each drum increased because they were moving in unison, a kind of sympathetic reinforcement, Teufel said.

Researchers looked for patterns in the returned signals or radar data. In the classical world, the results would be random. Plotting the results on a graph revealed unusual patterns suggesting the drums were entangled. To be certain, the researchers ran the experiment 10,000 times and applied a statistical test to calculate the correlations between various sets of results, such as the positions of the two drums.

"Roughly speaking, we measured how correlated two variables are -- for example if you measured the position of one drum, how well could you predict the position of the other drum," Teufel said. "If they have no correlations and they are both perfectly cold, you could only guess the average position of the other drum within an uncertainly of half a quantum of motion. When they are entangled, we can do better, with less uncertainty. Entanglement is the only way this is possible."

"To verify that entanglement is present, we do a statistical test called an 'entanglement witness,''' NIST theorist Scott Glancy said. "We observe correlations between the drums' positions and momentums, and if those correlations are stronger than can be produced by classical physics, we know the drums must have been entangled. The radar signals measure position and momentum simultaneously, but the Heisenberg uncertainty principle says that this can't be done with perfect accuracy. Therefore, we pay a cost of extra randomness in our measurements. We manage that uncertainty by collecting a large data set and correcting for the uncertainty during our statistical analysis."

Highly entangled, massive quantum systems like this might serve as long-lived nodes of quantum networks. The high-efficiency radar measurements used in this work could be helpful in applications such as quantum teleportation -- data transfer without a physical link -- or swapping entanglement between nodes of a quantum network, because these applications require decisions to be made based on measurements of entanglement outcomes. Entangled systems could also be used in fundamental tests of quantum mechanics and force sensing beyond standard quantum limits.

A new window to see hidden side of magnetized universe

Tyler O'Neal, Staff Editor VISUALIZATION

New observations and simulations show that jets of high-energy particles emitted from the central massive black hole in the brightest galaxy in galaxy clusters can be used to map the structure of invisible inter-cluster magnetic fields. These findings provide astronomers with a new tool for investigating previously unexplored aspects of clusters of galaxies.

As clusters of galaxies grow through collisions with surrounding matter, they create bow shocks and wakes in their dilute plasma. The plasma motion induced by these activities can drape intra-cluster magnetic layers, forming virtual walls of magnetic force. These magnetic layers, however, can only be observed indirectly when something interacts with them. Because it is simply difficult to identify such interactions, the nature of intra-cluster magnetic fields remains poorly understood. A new approach to map/characterize magnetic layers is highly desired. 

An international team of astronomers including Haruka Sakemi, a graduate student at Kyushu University (now a research fellow at the National Astronomical Observatory of Japan - NAOJ), used the MeerKAT radio telescope located in the Northern Karoo desert of South Africa to observe a bright galaxy in the merging galaxy cluster Abell 3376 known as MRC 0600-399. Located more than 600 million light-years away in the direction of the constellation Columba, MRC 0600-399 is known to have unusual jet structures bent to 90-degree angles. Previous X-ray observations revealed that MRC 0600-399 is the core of a sub-cluster penetrating the main cluster of galaxies, indicating the presence of strong magnetic layers at the boundary between the main and sub-clusters. These features make MRC 0600-399 an ideal laboratory to investigate interactions between jets and strong magnetic layers. The bent jet structures emitted from MRC 0600-399 as observed by the MeerKAT radio telescope (left) are well reproduced by the simulation conducted on ATERUI II (right). The nearby galaxy B visible in the left part of the MeerKAT image is not affecting the jet and has been excluded in the simulation. CREDIT Credit: Chibueze, Sakemi, Ohmura et al. (MeerKAT image); Takumi Ohmura, Mami Machida, Hirotaka Nakayama, 4D2U Project, NAOJ (ATERUI II image)

The MeerKAT observations revealed unprecedented details of the jets, most strikingly, faint "double-scythe" structure extending in the opposite direction from the bend points and creating a "T" shape. These new details show that, like a stream of water hitting a pane of glass, this is a very chaotic collision. Dedicated supercomputer simulations are required to explain the observed jet morphology and possible magnetic field configurations.

Takumi Ohmura, a graduate student at Kyushu University (now a research fellow at the University of Tokyo's Institute for Cosmic-Ray Research - ICRR), from the team performed simulations on NAOJ's supercomputer ATERUI II, the most powerful computer in the world dedicated to astronomical calculations. The simulations assumed an arch-like strong magnetic field, neglecting messy details like turbulence and the motion of the galaxy. This simple model provides a good match to the observations, indicating that the magnetic pattern used in the simulation reflects the actual magnetic field intensity and structure around MRC 0600-399. More importantly, it demonstrates that the simulations can successfully represent the underlying physics so that they can be used on other objects to characterize more complex magnetic field structures in clusters of galaxies. This provides astronomers with a new way to understand the magnetized Universe and a tool to analyze the higher-quality data from future radio observatories like the SKA (the Square Kilometre Array).

Johns Hopkins scientists model Saturn's interior

Tyler O'Neal, Staff Editor VISUALIZATION

Researchers simulate conditions necessary for the planet's unique magnetic field

New Johns Hopkins University simulations offer an intriguing look into Saturn's interior, suggesting that a thick layer of helium rain influences the planet's magnetic field.

The models, published this week in AGU Advances, also indicate that Saturn's interior may feature higher temperatures at the equatorial region, with lower temperatures at the high latitudes at the top of the helium rain layer.

It is notoriously difficult to study the interior structures of large gaseous planets, and the findings advance the effort to map Saturn's hidden regions. The magnetic field of Saturn seen at the surface. CREDIT Ankit Barik/Johns Hopkins University

"By studying how Saturn formed and how it evolved over time, we can learn a lot about the formation of other planets similar to Saturn within our own solar system, as well as beyond it," said co-author Sabine Stanley, a Johns Hopkins planetary physicist.

Saturn stands out among the planets in our solar system because its magnetic field appears to be almost perfectly symmetrical around the rotation axis. Detailed measurements of the magnetic field gleaned from the last orbits of NASA's Cassini mission provide an opportunity to better understand the planet's deep interior, where the magnetic field is generated, said lead author Chi Yan, a Johns Hopkins PhD candidate.

By feeding data gathered by the Cassini mission into powerful computer simulations similar to those used to study weather and climate, Yan and Stanley explored what ingredients are necessary to produce the dynamo--the electromagnetic conversion mechanism--that could account for Saturn's magnetic field.

"One thing we discovered was how sensitive the model was to very specific things like temperature," said Stanley, who is also a Bloomberg Distinguished Professor at Johns Hopkins in the Department of Earth & Planetary Sciences and the Space Exploration Sector of the Applied Physics Lab. "And that means we have a really interesting probe of Saturn's deep interior as far as 20,000 kilometers down. It's a kind of X-ray vision."

Strikingly, Yan and Stanley's simulations suggest that a slight degree of non-axisymmetry could actually exist near Saturn's north and south poles.

Saturn's interior with stably stratified Helium Insoluble Layer. CREDIT Yi Zheng (HEMI/MICA Extreme Arts Program)

"Even though the observations we have from Saturn look perfectly symmetrical, in our computer simulations we can fully interrogate the field," said Stanley.

Direct observation at the poles would be necessary to confirm it, but the finding could have implications for understanding another problem that has vexed scientists for decades: how to measure the rate at which Saturn rotates, or, in other words, the length of a day on the planet.