Tag Archives: state

Illustration by Michael S. Helfenbein

Yale physicists find a new form of quantum friction


Physicists at Yale University have observed a new form of quantum friction that could serve as a basis for robust information storage in quantum computers in the future. The researchers are building upon decades of research, experimentally demonstrating a procedure theorized nearly 30 years ago.

The results appear in the journal Science and are based on work in the lab of Michel Devoret, the F.W. Beinecke Professor of Applied Physics.

Quantum computers, a technology still in development, would rely on the laws of quantum mechanics to solve certain problems exponentially faster than classical computers. They would store information in quantum systems, such as the spin of an electron or the energy levels of an artificial atom. Called “qubits,” these storage units are the quantum equivalent of classical “bits.” But while bits can be in states like 0 or 1, qubits can simultaneously be in the 0 and 1 state. This property is called quantum superposition; it is a powerful resource, but also very fragile. Ensuring the integrity of quantum information is a major challenge of the field.

 Illustration by Michael S. Helfenbein
Illustration by Michael S. Helfenbein

Zaki Leghtas, first author on the paper and a postdoctoral researcher at Yale, offered the following metaphor to explain this new form of quantum friction:

Imagine a hill surrounded by two basins. If you put a ball at the top of the hill, it will roll down the sides and settle in one of the basins. As it rolls, it loses energy due to the friction between the ball and the ground, and it slows down. This is why it stops at the bottom of the basin. But friction also causes the ball to leave a path in its wake. By looking at either side of the hill and seeing where grass is flattened and stones are pushed aside, you can tell whether the ball rolled into the right or left basin.

This figure depicts the position of a quantum particle over a time of 19 micro-seconds. Dark colors indicate high probability of the particle existing at the specified position. It is a plot of the time-evolution of the Winger function W (⍺) of the quantum system, with black corresponding to 1.0, white to 0, and blue to –0.05.
This figure depicts the position of a quantum particle over a time of 19 micro-seconds. Dark colors indicate high probability of the particle existing at the specified position. It is a plot of the time-evolution of the Winger function W (⍺) of the quantum system, with black corresponding to 1.0, white to 0, and blue to –0.05.

If you replace the ball with a quantum particle, however, you run into a problem. Quantum particles can exist in many states at the same time, so in theory, the particle could occupy both basins simultaneously. But as the particle is rolling down, the friction between the particle and the hill leaves an impact on the environment, which can be measured. The same friction that stops the particle at the bottom also carves the path. This destroys the superposition and forces the particle to exist in only one basin.

Previously, researchers had been able to take advantage of this friction to trap quantum particles in particular basins. But now, Devoret’s lab demonstrates a new type of friction — one that slows the particle as it rolls, but does not carve a path that tells which side it is choosing. This allows the particle to simultaneously exist in both the left and right basins at the same time.

Each of these “basin” states is both stable and steady. While the quantum particle might move around in the basins, small perturbations won’t kick it out of the basins. Furthermore, any superpositions of these two basin states are also stable and steady. This means they could be used as a basis for storing quantum information.

Technically, this is called a two-dimensional quantum steady-state manifold. Devoret and Leghtas point out that the next step is expanding this two-dimensional manifold to four dimensions — adding two more basins to the landscape. This will allow scientists to redundantly encode quantum information and to do error correction within the manifold. Error correction is one of the key components that must be developed in order to make a practical quantum computer feasible.

Additional authors are Steven Touzard, Ioan Pop, Angela Kou, Brian Vlastakis, Andrei Petrenko, Katrina Sliwa, Anirudh Narla, Shyam Shankar, Michael Hatridge, Matthew Reagor, Luigi Frunzio, Robert Schoelkopf, and Mazyar Mirrahimi of Yale. Mirrahimi also has an appointment at the Institut National de Recherche en Informatique et en Automatique Paris-Rocquencourt.

(Main illustration by Michael S. Helfenbein)

Source: Yale News

KAUST team synthesizes novel metal-organic framework for efficient CO2 removal

By Caitlin Clark

“In Professor Mohamed Eddaoudi’s research group, we are always on the quest to find novel nanostructured functionalized materialsfor specific applications,” explained KAUST Research Scientist Dr. Youssef Belmabkhout, a member of Prof. Eddaoudi’s Functional Materials Design, Discovery, and Development (FMD3) group, part of KAUST’s Advanced Membranes and Porous Materials (AMPM) research center.

Dr. Osama Shekhah, Senior Research Scientist in the FMD3 group added that the group searches “for materials that will be highly suitable for trace and low CO2 concentration removal using purely physical adsorption. These will help in energy saving and in the reduction of the cost of the production, purification, and enrichment of highly valuable commodities such as CH4, H2, O2, N2, and others.”

Drs. Shekhah and Belmabkhout and a team of researchers from Prof. Eddaoudi’s group recently discovered and synthesized a new porous, moisture-resistant, inexpensive and reusable copper-based metal-organic framework (MOF) called SIFSIX-3-Cu that can selectively adsorb and remove trace CO2 from mixtures of various gases. Their findings were published in the June 25 edition of Nature Communications (DOI: 10.1038/ncomms5228).

MOFs are a promising new class of hybrid solid-state materials for CO2 removal. “Their uniqueness,” explained Prof. Eddaoudi, “resides in the ability to control their assembly and introduce functionality on demand. This feature is not readily available in other solid-state materials.”

The researchers showed for the first time that MOF crystal chemistry permits the assembly of a new isostructural hexafluorosilicate MOF (SIFSIX-3-Cu) based on copper instead of zinc.

“This technology is anticipated to outperform the existing mature technologies for CO2 physical adsorption in terms of energy efficiency,” says Dr. Shekhah. “The key factors for this finding are the combination of suitable pore size and high, uniform charge density in the pores of the MOF.”

Using their newly synthesized MOF, the researchers examined the conditions relevant to direct air capture (DAC), a mechanism to remove CO2 from air and reduce greenhouse gas emissions uniformly around the world.

DAC is more challenging than post-combustion capture, but it may be practical if alternative “suitable adsorbent combining optimum uptake, kinetics, energetics and CO2 selectivity is available at trace CO2 concentration,” the researchers stated.

The team discovered that contracting SIFSIX-3-Cu’s pore system to 3.5 Å enhanced the material’s efficiency, making it able to adsorb relatively large CO2 amounts 10-15 times higher than zinc-based metal-organic adsorbents, such as SIFSIX-3-Zn. In SIFSIX-3-Zn, the pore size is 3.84 Å.

“We attribute this property to enhanced physical sorption through the favorable electrostatic interactions between CO2 molecules and fluorine atoms present on the surface of the adsorbent,” explained Zhijie Chen, a Ph.D. student in the FMD3 group and a co-author of the paper.

Dr. Vincent Guillerm, a post-doctoral fellow in the FMD3 group and a co-author of the paper also noted that, “the pore contraction gives CO2 uptake and selectivity at very low partial pressures. This is relevant to DAC and trace carbon dioxide removal.”

“SIFSIX-3-Cu gives enhanced CO2 physical adsorption properties, uptake, and selectivity in highly diluted gas streams, and this performance is unachievable with other classes of porous materials,” added Dr. Karim Adil, a co-author of the paper and Research Scientist in the FMD3 group.

The researchers are excited about their finding as it offers the potential to be used not only for DAC but also for other applications related to energy, the environment, and the healthcare field. For example, SIFSIX-3-Cu could be used to remove and recycle CO2 in confined spaces, such as in submarines or space shuttles, and could also be used in anesthesia machines, which require efficient CO2 sorbents.

“Our work paves the way for scientists to develop new separation agents suitable for challenging endeavor pertaining to CO2 ultra-purification processing,” said Dr. Shekhah. “Our study is also part of a greater critical effort to develop economical and practical pathways to reduce cumulative CO2 emissions provoking the undesirable greenhouse gas effect.”

Prof. Eddaoudi reiterated that “MOFs offer remarkable CO2 physical adsorption attributes in highly diluted gas streams thanks to their ability for rational pore size modification and inorganic-organics moieties substitution. Other classes of plain materials are unable to attain this.”

In the future, Prof. Eddaoudi’s FMD3 group will continue to develop topologically and chemically different MOFs. “We aim to target novel MOFs with suitable pore size and high charge density,” explained Prof. Eddaoudi. “We will then use these for the important task of removing trace and low and high concentration CO2.”

Source: KAUST