Tag Archives: Tongcang Li

World’s smallest disco party features nanoscale disco ball

I haven’t featured one of these ‘fun’ (world’s smallest xxx) announcements in a long time. An August 14, 2024 news item on phys.org announces the world’s smallest disco party and a step towards exploring quantum gravity, Note: Links have been removed,

Physicists at Purdue [Purdue University, Indiana, US] are throwing the world’s smallest disco party. The disco ball itself is a fluorescent nanodiamond, which they have levitated and spun at incredibly high speeds. The fluorescent diamond emits and scatters multicolor lights in different directions as it rotates. The party continues as they study the effects of fast rotation on the spin qubits within their system and are able to observe the Berry phase.

The team, led by Tongcang Li, professor of Physics and Astronomy and Electrical and Computer Engineering at Purdue University, published their results in Nature Communications. Reviewers of the publication described this work as “arguably a groundbreaking moment for the study of rotating quantum systems and levitodynamics” and “a new milestone for the levitated optomechanics community.”

This graph illustrates a diamond particle levitated above a surface ion trap. The fluorescent diamond nanoparticle is driven to rotate at a high speed (up to 1.2 billion rpm) by alternating voltages applied to the four corner electrodes. This rapid rotation induces a phase in the nitrogen-vacancy electron spins inside the diamond. The diagram in the top left corner depicts the atomic structure of a nitrogen-vacancy spin defect inside the diamond. Graphic provided by Kunhong Shen.

An August 13, 2024 Purdue University news release (also on EurekAlert but published August 14, 2024) by Cheryl Pierce, which originated the news item, explains what makes this work so exciting (!), Note: Links have been removed,

“Imagine tiny diamonds floating in an empty space or vacuum. Inside these diamonds, there are spin qubits that scientists can use to make precise measurements and explore the mysterious relationship between quantum mechanics and gravity,” explains Li, who is also a member of the Purdue Quantum Science and Engineering Institute.  “In the past, experiments with these floating diamonds had trouble in preventing their loss in vacuum and reading out the spin qubits. However, in our work, we successfully levitated a diamond in a high vacuum using a special ion trap. For the first time, we could observe and control the behavior of the spin qubits inside the levitated diamond in high vacuum.”

The team made the diamonds rotate incredibly fast—up to 1.2 billion times per minute! By doing this, they were able to observe how the rotation affected the spin qubits in a unique way known as the Berry phase.

“This breakthrough helps us better understand and study the fascinating world of quantum physics,” he says.

The fluorescent nanodiamonds, with an average diameter of about 750 nm, were produced through high-pressure, high-temperature synthesis. These diamonds were irradiated with high-energy electrons to create nitrogen-vacancy color centers, which host electron spin qubits. When illuminated by a green laser, they emitted red light, which was used to read out their electron spin states. An additional infrared laser was shone at the levitated nanodiamond to monitor its rotation. Like a disco ball, as the nanodiamond rotated, the direction of the scattered infrared light changed, carrying the rotation information of the nanodiamond.

The authors of this paper were mostly from Purdue University and are members of Li’s research group: Yuanbin Jin (postdoc), Kunhong Shen (PhD student), Xingyu Gao (PhD student) and Peng Ju (recent PhD graduate). Li, Jin, Shen, and Ju conceived and designed the project and Jin and Shen built the setup. Jin subsequently performed measurements and calculations and the team collectively discussed the results. Two non-Purdue authors are Alejandro Grine, principal member of technical staff at Sandia National Laboratories, and Chong Zu, assistant professor at Washington University in St. Louis. Li’s team discussed the experiment results with Grine and Zu who provided suggestions for improvement of the experiment and manuscript.

“For the design of our integrated surface ion trap,” explains Jin, “we used a commercial software, COMSOL Multiphysics, to perform 3D simulations. We calculate the trapping position and the microwave transmittance using different parameters to optimize the design. We added extra electrodes to conveniently control the motion of a levitated diamond. And for fabrication, the surface ion trap is fabricated on a sapphire wafer using photolithography. A 300-nm-thick gold layer is deposited on the sapphire wafer to create the electrodes of the surface ion trap.”

So which way are the diamonds spinning and can they be speed or direction manipulated? Shen says yes, they can adjust the spin direction and levitation.

“We can adjust the driving voltage to change the spinning direction,” he explains. “The levitated diamond can rotate around the z-axis (which is perpendicular to the surface of the ion trap), shown in the schematic, either clockwise or counterclockwise, depending on our driving signal. If we don’t apply the driving signal, the diamond will spin omnidirectionally, like a ball of yarn.”

Levitated nanodiamonds with embedded spin qubits have been proposed for precision measurements and creating large quantum superpositions to test the limit of quantum mechanics and the quantum nature of gravity.

“General relativity and quantum mechanics are two of the most important scientific breakthroughs in the 20th century. However, we still do not know how gravity might be quantized,” says Li. “Achieving the ability to study quantum gravity experimentally would be a tremendous breakthrough. In addition, rotating diamonds with embedded spin qubits provide a platform to study the coupling between mechanical motion and quantum spins.”

This discovery could have a ripple effect in industrial applications. Li says that levitated micro and nano-scale particles in vacuum can serve as excellent accelerometers and electric field sensors. For example, the US Air Force Research Laboratory (AFRL) are using optically-levitated nanoparticles to develop solutions for critical problems in navigation and communication.

“At Purdue University, we have state-of-the-art facilities for our research in levitated optomechanics,” says Li. “We have two specialized, home-built systems dedicated to this area of study. Additionally, we have access to the shared facilities at the Birck Nanotechnology Center, which enables us to fabricate and characterize the integrated surface ion trap on campus. We are also fortunate to have talented students and postdocs capable of conducting cutting-edge research. Furthermore, my group has been working in this field for ten years, and our extensive experience has allowed us to make rapid progress.”

Quantum research is one of four key pillars of the Purdue Computes initiative, which emphasizes the university’s extensive technological and computational environment.

This research was supported by the National Science Foundation (grant number PHY-2110591), the Office of Naval Research (grant number N00014-18-1-2371), and the Gordon and Betty Moore Foundation (grant DOI 10.37807/gbmf12259). The project is also partially supported by the Laboratory Directed Research and Development program at Sandia National Laboratories.

Here’s a link to and a citation for the paper,

Quantum control and Berry phase of electron spins in rotating levitated diamonds in high vacuum by Yuanbin Jin, Kunhong Shen, Peng Ju, Xingyu Gao, Chong Zu, Alejandro J. Grine & Tongcang Li. Nature Communications volume 15, Article number: 5063 (2024) DOI: https://doi.org/10.1038/s41467-024-49175-3 Published online: 13 June 2024

This paper is open access.

Space-time crystals and everlasting clocks

Apparently, a space-time crystal could be useful for such things as studying the many-body problem in physics.  Since I hadn’t realized the many-body problem existed and have no idea how this might affect me or anyone else, I will have to take the utility of a space-time crystal on trust.As for the possibility of an everlasting clock, how will I ever know the truth since I’m not everlasting?

The Sept. 24, 2012 news item on Nanowerk about a new development makes the space-time crystal sound quite fascinating,

Imagine a clock that will keep perfect time forever, even after the heat-death of the universe. This is the “wow” factor behind a device known as a “space-time crystal,” a four-dimensional crystal that has periodic structure in time as well as space. However, there are also practical and important scientific reasons for constructing a space-time crystal. With such a 4D crystal, scientists would have a new and more effective means by which to study how complex physical properties and behaviors emerge from the collective interactions of large numbers of individual particles, the so-called many-body problem of physics. A space-time crystal could also be used to study phenomena in the quantum world, such as entanglement, in which an action on one particle impacts another particle even if the two particles are separated by vast distances. [emphasis mine]

While I’m most interested in the possibility of studying entanglement, it seems to me the scientists are guessing since the verb ‘could’ is being used where they used ‘would’ previously for studying the many body problem.

The Sept. 24, 2012 news release by Lynn Yarris for the Lawrence Berkeley National Laboratory  (Berkeley Lab), which originated the news item, provides detail on the latest space-time crystal development,

A space-time crystal, however, has only existed as a concept in the minds of theoretical scientists with no serious idea as to how to actually build one – until now. An international team of scientists led by researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has proposed the experimental design of a space-time crystal based on an electric-field ion trap and the Coulomb repulsion of particles that carry the same electrical charge.

“The electric field of the ion trap holds charged particles in place and Coulomb repulsion causes them to spontaneously form a spatial ring crystal,” says Xiang Zhang, a faculty scientist  with Berkeley Lab’s Materials Sciences Division who led this research. “Under the application of a weak static magnetic field, this ring-shaped ion crystal will begin a rotation that will never stop. The persistent rotation of trapped ions produces temporal order, leading to the formation of a space-time crystal at the lowest quantum energy state.”

Because the space-time crystal is already at its lowest quantum energy state, its temporal order – or timekeeping – will theoretically persist even after the rest of our universe reaches entropy, thermodynamic equilibrium or “heat-death.”

This new development builds on some work done earlier this year at the Massachusetts Institute of Technology (MIT), from the Yarris news release,

The concept of a crystal that has discrete order in time was proposed earlier this year by Frank Wilczek, the Nobel-prize winning physicist at the Massachusetts Institute of Technology. While Wilczek mathematically proved that a time crystal can exist, how to physically realize such a time crystal was unclear. Zhang and his group, who have been working on issues with temporal order in a different system since September 2011, have come up with an experimental design to build a crystal that is discrete both in space and time – a space-time crystal.

Traditional crystals are 3D solid structures made up of atoms or molecules bonded together in an orderly and repeating pattern. Common examples are ice, salt and snowflakes. Crystallization takes place when heat is removed from a molecular system until it reaches its lower energy state. At a certain point of lower energy, continuous spatial symmetry breaks down and the crystal assumes discrete symmetry, meaning that instead of the structure being the same in all directions, it is the same in only a few directions.

“Great progress has been made over the last few decades in exploring the exciting physics of low-dimensional crystalline materials such as two-dimensional graphene, one-dimensional nanotubes, and zero-dimensional buckyballs,” says Tongcang Li, lead author of the PRL paper and a post-doc in Zhang’s research group. “The idea of creating a crystal with dimensions higher than that of conventional 3D crystals is an important conceptual breakthrough in physics and it is very exciting for us to be the first to devise a way to realize a space-time crystal.”

Just as a 3D crystal is configured at the lowest quantum energy state when continuous spatial symmetry is broken into discrete symmetry, so too is symmetry breaking expected to configure the temporal component of the space-time crystal. Under the scheme devised by Zhang and Li and their colleagues, a spatial ring of trapped ions in persistent rotation will periodically reproduce itself in time, forming a temporal analog of an ordinary spatial crystal. With a periodic structure in both space and time, the result is a space-time crystal.

Here’s an image created by team at the Berkeley Lab to represent their work on the space-time crystal,

Imagine a clock that will keep perfect time forever or a device that opens new dimensions into quantum phenomena such as emergence and entanglement. (courtesy of Xiang Zhang group[?] at Berkeley Lab)

For anyone who’s interested in this work, I suggest reading either the news item on Nanowerk or the Berkeley Lab news release in full. I will leave you with Natalie Cole and Everlasting Love,