A new project will use the electric field in an accelerator cavity to try to
levitate a tiny metallic particle, allowing it to store quantum information
Quantum computing could solve problems that are difficult for traditional
computer systems. It may seem like magic. One step toward achieving quantum
computing even resembles a magician’s trick: levitation. A new project at
the U.S. Department of Energy’s Thomas Jefferson National Accelerator
Facility will attempt this trick by levitating a microscopic particle in a
superconducting radiofrequency (SRF) cavity to observe quantum
phenomena.
Typically at Jefferson Lab and other particle accelerator facilities, SRF
cavities enable studies of the atom’s nucleus. They do this by accelerating
subatomic particles, such as electrons. This project will use the same type
of cavity to instead levitate a microscopic particle of metal, between 1 and
100 micrometers in diameter, with the cavity’s electric field.
“No one has ever intentionally suspended a particle in an electric field in
a vacuum using SRF cavities,” said Drew Weisenberger, a principal
investigator on this project, as well as Chief Technology Officer and head
of the Radiation Detector and Imaging Group in the Experimental Nuclear
Physics Division at Jefferson Lab.
If the project team is able to levitate a particle, they might be able to
then impart a quantum state on it by cooling the trapped particle to its
lowest possible energy level (because that’s when quantum properties occur).
“Storing quantum information on a levitated nanoparticle is our ultimate
goal, but for now, it is a proof of principle experiment,” said Pashupati
Dhakal, another principal investigator on the project and a staff scientist
at Jefferson Lab in the Accelerator Operations, Research and Development
Division. “We want to know if we can trap and levitate particles inside the
cavity using the electric field.”
Exploring the Quantum with Accelerator Cavities
The idea for this project came from observations of accelerator experts.
They think they have already unintentionally levitated unwanted and rare
nanoparticles of metal, such as niobium and iron, inside SRF cavities during
particle accelerator operations. They suspect that this unintentional
levitation has impacted the performance of SRF cavity components.
Researchers are attempting to use a several-decades-old technique called
“laser trapping”, as a step toward reliably imparting a quantum state on a
particle suspended in a laser beam. But, the Jefferson Lab project team
thinks that SRF cavities may provide a better tool for those researchers.
“An electric field could go potentially beyond the capabilities of laser
trapping,” Weisenberger said.
Intrinsic characteristics of SRF cavities will overcome some limits of laser
trapping. A levitated particle in an SRF cavity that is under vacuum and
chilled to super cold temperatures will only interact with the cavity’s
electric field and not lose information to the outside, which is important
for maintaining a quantum state.
“Like storing information on a computer chip, the quantum state will stay
and not dissipate,” Weisenberger said. “And that could eventually lead to
applications in quantum computing and quantum communications.”
This project, titled “SRF Levitation and Trapping of Nanoparticles
Experiment,” is funded by the Laboratory Directed Research & Development
program, which provides resources for Jefferson Lab personnel to make rapid
and significant contributions to critical science and technology problems
relevant to the mission of Jefferson Lab and the DOE.
A Multidisciplinary Approach
The project was conceived and launched by Rongli Geng in October 2021 before
he transitioned to Oak Ridge National Laboratory. It has now shifted to a
larger and more multi-disciplinary team led by Weisenberger and Dhakal, the
current co-principal investigators.
Weisenberger’s team researches detector technology for nuclear physics
research, whereas Dhakal’s work focuses on developing SRF cavities to
accelerate electrons at high speeds. Weisenberger says that the
multidisciplinary approach will bring together their expertise as they
branch out together into the less familiar territory of this LDRD project.
Both principal investigators remark that the project is moving forward well,
thanks to the diligence and expertise supplied by every member of the team.
Team members include John Musson, Frank Marhauser, Haipeng Wang, Wenze Xi,
Brian Kross and Jack McKisson.
“It’s an interesting step outside of the usual things that we do,”
Weisenberger said. “The LDRD program lets loose Jefferson Lab scientists and
engineers on a research question that isn’t directly related to what we’re
actually hired to do, but is making use of all the expertise that we bring
and it’s a great resource to tap to try to stretch. That’s what we’re doing
with this project, stretching.”
Building and Testing
Before turning the project over the Weisenberger and Dhakal, Geng and his
colleagues had determined the required parameters of the cavity and electric
field with simulations and calculations.
“We have everything on paper but we have to make it into a reality,” Dhakal
said.
The team is currently setting up the experiment in real life.
“We have to see if what was simulated can actually happen,” Weisenberger
said.
First, they’ll assemble a mock-up of the experiment at room temperature.
Then, they’ll circulate liquid helium around the outer surfaces of the
cavity to cool it to superconducting temperatures approaching absolute zero.
Next comes the most difficult part. They must get a single microscopic
particle in the correct region of the cavity while the cavity is locked up
inside a containment vessel at superconducting temperatures, under vacuum,
and with the electric field on.
“We’ve come up with a way to remotely launch a particle in the cavity under
experimental conditions, we just have to test it now,” Weisenberger said.
“In the research and development world, you often can’t do what you thought
you could do. We try and test and run into problems, try to solve the
problems, and keep going.”
This is a year-long project with the possibility of another year of funding,
depending on how things go. It is also an early stage, proof of principle
project. If it is ultimately successful, there would still be a long road of
R&D before the concepts could be applied toward building quantum
computers. Such computers would require levitating and imparting quantum
states on tens to hundreds to thousands of much smaller particles
predictably and reliably.
Still, the researchers are looking forward to the discoveries they hope this
study will enable regarding microscopic particle levitation and potential
observation of a quantum state.
“I’m optimistic,” Dhakal said. “Either way, we’ll discover something.
Failure is just as much a part of R&D as success. You learn from both.
Basically, whether the particle levitates or not, or whether we can impart
the quantum state to it or not, it’s something that’s never been done
before. It’s very challenging and exciting.”
The team already has a research paper in the works for this project, but
only time will tell whether they can realize this bit of magic in the
laboratory.
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