Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Control scheme dynamically maintains unstable quantum system

Quantum inverted pendulum

A simple pendulum has two equilibrium points: hanging in the "down" position and perfectly inverted in the "up" position. While the "down" position is a stable equilibrium, the inverted position is definitely not stable. Any infinitesimal deviation from perfectly inverted is enough to cause the pendulum to eventually swing down.

Georgia Tech professor Michael Chapman poses with laser equipment in his laboratory. Georgia Tech researchers have demonstrated a way to maintain an unstable quantum system by applying bursts of microwave radiation.

Credit: Georgia Tech Photo: John Toon

It has been known for more than 100 years, though, that an inverted pendulum can be stabilized by vibrating the pivot point. This non-intuitive phenomenon is known as dynamic stabilization, and it has led to a broad range of applications including charged particle traps, mass spectrometers and high-energy particle accelerators.

Many-body quantum systems can also be placed into unstable non-equilibrium states, and like the inverted pendulum of classical physics, they typically evolve away from these states. Now, researchers at the Georgia Institute of Technology have demonstrated a way to maintain an unstable quantum system by applying bursts of microwave radiation – a quantum analog to vibrating the inverted pendulum.

In an experiment that could have implications for quantum computers and quantum simulators, the researchers used microwave pulses of varying amplitudes and frequencies to control a quantum system composed of a cloud of approximately 40,000 rubidium atoms cooled nearly to absolute zero.

The research, sponsored by the National Science Foundation and reported online August 27 by the journal Physical Review Letters, experimentally demonstrated dynamical stabilization of a non-equilibrium many-body quantum system. The paper is scheduled to appear in the journal's August 30 print issue.

"In this work, we have demonstrated that we can control the quantum dynamics of a cloud of atoms to maintain them in a non-equilibrium configuration analogous to the inverted pendulum," said Michael Chapman, a professor in the Georgia Tech School of Physics. "What we actually control is the internal spins of the atoms that give each atom a small magnetic moment. The spins are oriented in an external magnetic field against their will such that they would prefer to flip their orientation to the equilibrium position."

Mathematically, the state of the rubidium atoms is virtually identical to that of the simple mechanical pendulum, meaning that Chapman and his students have controlled what could be called a "quantum inverted pendulum."

In their experiment, the researchers began with a spin-1 atomic Bose-Einstein condensate (BEC) that is initialized in an unstable, fixed point of the spin-nematic phase space – comparable to an inverted pendulum. If allowed to freely evolve, interactions between the atoms would give rise to squeezing, quantum spin mixing and eventually relaxation to a stable state – comparable to a pendulum hanging straight down from a pivot point.

By periodically applying bursts of microwave radiation, the researchers rotated the spin-nematic many-body fluctuations, halting the squeezing and the relaxation toward stability. The researchers investigated a range of pulse periods and phase shifts to map a stability diagram that compares well with what they expected theoretically.

"The net effect is that the many-body system basically returns to the original state," said Chapman. "We reverse the squeezing of the condensate, and after it again evolves toward squeezing, we cause it to return. If we do this periodically, we can maintain the Bose-Einstein condensate in this unstable point indefinitely."

The control technique differs from active feedback, which measures the direction in which a system is moving and applies a force counter to that direction. The open-loop technique used by Chapman's group applies a constant input that doesn't vary with the activity of the system being controlled.

"We are periodically kicking the system to keep it in a state where it doesn't want to be," he said. "This is the first time we have been able to make a many-body spin system that we can stabilize against its natural evolution."

Controlling and manipulating single-particle quantum systems or simple collections of atoms, electrons and photons has been a focus of the physics community over recent decades. These capabilities have formed the foundation for technologies such as lasers, magnetic resonance imaging, atomic clocks and new atomic sensors for magnetic fields and inertial guidance.

Now, researchers are studying more complex systems that involve many additional interacting particles, perhaps thousands of them. Chapman and his group hope to help extend their knowledge of these more complex many-body systems, which could lead to developments in quantum computing, quantum simulations and improved measurements.

"The long-range goal of our work is to further the understanding of quantum mechanics and to develop new technologies that exploit the often counterintuitive realities of the quantum world," Chapman said. "Quantum many-body systems are being actively explored, and one of the things you'd like to do is be able to control them. I think this is one of the cleanest examples of being able to control a quantum many-body system in a manifestly unstable configuration."

In addition to Chapman, other co-authors of the paper include T.M. Hoang, C.S. Gerving, B.J. Land, M. Anquez and C.D. Hamley.

This research is supported by the National Science Foundation (NSF) under Award PHY-1208828. Any conclusions or opinions are those of the authors and do not necessarily represent the official views of the NSF.

John Toon | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)

nachricht Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>