Tyler O'Neal, Staff Editor ACADEMIA

Flawed diamonds may provide perfect interface for quantum supercomputers

Flaws in diamonds, atomic defects where carbon is replaced by nitrogen or another element, may offer a close-to-perfect interface for quantum supercomputing, a proposed communications exchange that promises to be faster and more secure than current methods. There’s one major problem, though: these flaws, known as diamond nitrogen-vacancy centers, are controlled via a magnetic field, which is incompatible with existing quantum devices. Imagine trying to connect an Altair, an early personal computer developed in 1974, to the internet via WiFi. It’s a difficult, but not impossible task. The two technologies speak different languages, so the first step is to help translate. By combining the entangled emission demonstrated in this study with the previously demonstrated quantum teleportation transfer from a photon to a nuclear spin in diamond, researchers will generate quantum entanglement between remote locations based on quantum teleportation.

Researchers at Yokohama National University have developed an interface approach to control the diamond nitrogen-vacancy centers in a way that allows direct translation to quantum devices. 

“To realize the quantum internet, a quantum interface is required to generate remote quantum entanglement by photons, which are a quantum communication medium,” said corresponding author Hideo Kosaka, professor in the Quantum Information Research Center, Institute of Advanced Sciences and in the Department of Physics, Graduate School of Engineering, both at Yokohama National University. “

The promised quantum internet is rooted in more than a century’s worth of work in which researchers determined that photons are both particles and waves of light simultaneously — and that their wave state can reveal information about their particle state and vice versa. More than that, the two states could influence each other: pinching the wave could bruise the particle, so to speak. Their very nature is entangled, even across vast distances. The aim is to control the entanglement to communicate discrete data instantaneously and securely.

Previous research has demonstrated this controlled entanglement can be achieved by applying a magnetic field to the nitrogen-vacancy centers, Kosaka said, but a non-magnetic field approach is needed to move closer to realizing the quantum internet.

His team successfully used microwave and light polarized waves to entangle an emitted photon and left spin qubits, the quantum equivalent of information bits in classical systems. These polarizations are waves that move perpendicular to the originating source, like seismic waves radiating out horizontally from a vertical fault shift. In quantum mechanics, the spin property — either right- or left-handed — of the photon determines how the polarization moves, meaning it is predictable and controllable. Critically, according to Kosaka, when inducing entanglement via this property under a non-magnetic field, the connection appears steadfast against other variables.

“The geometric nature of polarization allows us to generate remote quantum entanglement that is resilient to noise and timing errors,” Kosaka said. 

According to Kosaka, his team will combine this approach with a previously demonstrated quantum information transfer via teleportation to generate quantum entanglement, and the resulting exchange of information, between remote locations. The eventual goal, Kosaka said, is to facilitate a connected network of quantum computers to establish a quantum internet.

“The realization of a quantum internet will enable quantum cryptography, distributed quantum computation, and quantum sensing over long distances of more than 1,000 kilometers,” Kosaka said.

Rochester scientists reveal the limits of machine learning for hydrogen models

Tyler O'Neal, Staff Editor ACADEMIA

Research from the Laboratory for Laser Energetics paves the way for more accurate supercomputer models, which are needed to understand the interior of planets and the physical properties of nuclear fusion. Metallic hydrogen is rare on earth, but it is found in large quantities in the interiors of planets such as Jupiter. New research at the Laboratory for Laser Energetics provides more accurate data on hydrogen's phase transition to metallic hydrogen, which will help in building more accurate computer models. (NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill)

Hydrogen is one of the most abundant elements in the universe.

On Earth, hydrogen is normally a gas. But when it is under high temperatures and pressures—the conditions that exist within many planets, such as Jupiter—hydrogen goes through a series of phase transitions and takes on the properties of a liquid metal. One of the metallic properties it takes on is becoming an electrical conductor.

In a new paper in Nature’s “Matters Arising,” researchers at the University of Rochester Laboratory for Laser Energetics (LLE), including lead author Valentin Karasiev, an LLE staff scientist; graduate student Josh Hinz; and Suxing Hu, an associate professor of mechanical engineering and a distinguished scientist at the LLE, respond to a 2020 Nature paper that used machine learning techniques to study the liquid-liquid phase transitions of dense hydrogen from an insulating liquid to a liquid metal.

In their response, Karasiev and his colleagues outline how these machine learning techniques produced incorrect results in describing hydrogen’s phase transitions. Their research has important implications in building more accurate computer models to study hydrogen, which can lead to a better understanding of the interiors of planets and stars and the physical properties of processes like nuclear fusion.

When building the equation-of-state of hydrogen—the equation that describes the state of hydrogen under various physical conditions—it is important to characterize the transition into the metallic hydrogen phase: Is it an abrupt (sharp) transition or a smooth transition?

“This physics character of first-order phase transition can have profound implications in understanding what giant planets’ interior structures look like, such as de-mixing of hydrogen and helium in Jupiter,” Hu says.

In the 2020 Nature paper, researchers used machine learning and concluded the transition of hydrogen to the metallic hydrogen phase was smooth. Karasiev and his colleagues, however, performed large-scale quantum simulations using other fundamental density-functional theories and found that hydrogen’s transition is not smooth, but is instead more abrupt. This is consistent with other previous data collected without machine learning.

“Our work demonstrated that machine learning can fool scientists if they are not careful when using machine learning to study phase-transition boundaries,” Karasiev says. “This is an important step in building better models to outline how hydrogen can become metallic hydrogen.”

Scientists unravel a new insight into how Pluto has formed ice-shapes

Tyler O'Neal, Staff Editor ACADEMIA

A team of international researchers, including Dr. Adrien Morison from the University of Exeter, has shown how vast ice forms have been shaped in one of the planet’s largest craters, Sputnik Planitia.  web pluto nasa rh 218xfree fee28

Perhaps the most striking feature on Pluto’s surface, Sputnik Planitia is an impact crater, consisting of a bright plain, slightly larger than France, and filled with nitrogen ice. 

For the new study, researchers have used sophisticated supercomputer modeling techniques to show that these ice forms, polygonal in shape, are formed by the sublimation of ice – a phenomenon where the solid ice can turn into a gas without going through a liquid state. 

The research team shows this sublimation of the nitrogen ice powers convection in the ice layer of Sputnik Planitia by cooling down its surface.  

Dr. Morison, a Research Fellow from Exeter’s Physics and Astronomy department said: “When the space probe New Horizon performed the only, to date, fly-by of Pluto in 2015, the collected data was enough to drastically change our understanding of this remote world.  

“In particular, it showed that Pluto is still geologically active despite being far away from the Sun and having limited internal energy sources. This included at Sputnik Planitia,  where the surface conditions allow the gaseous nitrogen in its atmosphere to coexist with solid nitrogen.  

“We know that the surface of the ice exhibits remarkable polygonal features – formed by thermal convection in the nitrogen ice, constantly organizing and renewing the surface of the ice.  However, there remained questions behind just how this process could occur.” 

In the new study, the research team conducted a series of numerical simulations that showed that cooling from sublimation can power convection in a way that is consistent with numerous data coming from New Horizons  - including the size of polygons, amplitude of topography, and surface velocities. 

It is also consistent with the timescale at which climate models predict sublimation of Sputnik Planitia, beginning around 1 - 2 million years ago. It showed that the dynamics of this nitrogen ice layer echo those found on Earth’s oceans, being driven by the climate.  

Such climate-powered dynamics of a solid layer could also occur at the surface of other planetary bodies, such as Triton (one of Neptune’s moons), or Eris and Makemake (from Kuiper’s Belt). 

Sublimation-driven convection in Sputnik Planitia on Pluto, by Dr. Morison (University of Exeter), Pr Labrosse (Geology Laboratory of Lyon, France), and Dr. Choblet (Planetology and Geodynamics Laboratory of Nantes, France) is published in Nature.