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FQXI ARTICLE

July 1, 2015

Quantum Upsizing

Mirror, mirror on the wall, what is the largest quantum object of them all? Aspelmeyer, Schwab, and Zeilinger have teamed up to find out.

August 15, 2008

ANTON ZEILINGER

University of Vienna

Credit: Jaqueline Godany

Defying the standard wisdom of the nanotechnology crowd, the team wants to scale their nanotools up. They hope to create quantum effects in ever larger objects, to test how far they can push the boundary between the quantum and classical realms.

But that’s only part of it. Stretching across continents, the collaboration itself is an exercise in bigger and better. Schwab and a small army of grad students operate out of his lab at Cornell University in Ithaca, New York, while Aspelmeyer, Zeilinger, and another crew of grad students work in Austria, at the University of Vienna. The group leaders rarely see each other face-to-face, yet they regularly share ideas, students, and even lab equipment.

Quantum effects are mysterious, says Schwab. "Why do they work on a small scale but not at a big scale?" This, he says, is the major question that the group plans to answer: "Can we start to observe quantum behavior in bigger and bigger objects?"

Quantum Breakdown

To investigate where quantum mechanics breaks down and classical mechanics begins, the team is investigating two weird quantum properties:

Can we start to

observe quantum

behavior in bigger

and bigger objects?

observe quantum

behavior in bigger

and bigger objects?

- Keith Schwab

In the quest to do this, Aspelmeyer is using micro-mirrors, just half a millimeter across and a hundredth of a millimeter wide, to pick up quantum effects. That may sound small, but one micro-mirror contains billions of atoms, making the system several orders of magnitude larger and more complex than anything that has been used to test quantum mechanics before. The team will bounce entangled photons off the mirrors. The trick is to see if the photons transfer their quantum nature to the mirror.

Micro Diving Boards

"If one photon hits the mirror, it kicks the mirror, which then oscillates with a certain amplitude," says Aspelmeyer. He likens the situation to the motion of a diving board. "If there were two people on the diving board it goes up and down more strongly," he says. Similarly, you can work out how many photons have hit the mirror, by how much it vibrates.

Sounds straightforward. But what happens if the number of photons that hit the mirror is not an exact number?

KEITH SCHWAB

Cornell University

For the experiment to work, the researchers need to keep their cool—or at least, keep their apparatus at a low temperature because heat causes the mirror to shake on its own. This is where Schwab comes in. Not only will Schwab build the micro-mirror at his lab, he has also spent years using cryogenics and laser cooling trying to get tiny mechanical systems as cold as possible. One of the techniques used to cool particles (and small mechanical devices) is to hit them with laser light. When hit with just the right frequency of laser light, the particles temporarily absorb the light, gaining energy. However, they quickly lose this again, releasing more energy than they absorbed in the process, and cooling down to a temperature that is lower than where they started.

Quantum Milestones

Using this technique and others, Schwab has cooled mechanical devices to just above their lowest possible energy level, known as the ground state. "We want to hit some basic quantum mechanical milestones like cooling mechanical devices with light down to ground state," said Schwab. Zeilinger was the matchmaker who brought Schwab and Aspelmeyer together. He believes they work so well together not only because they share the same interest but also because "their personalities get along well together."

"Coming from different backgrounds there are so many different things to share and exchange," says Aspelmeyer. "We have learned a great deal from Keith already concerning mechanical systems and low temperature physics, and there were many good discussions where the quantum optics from our side brought new perspective to the experiments."

We want to hit

some basic quantum

mechanical milestones.

some basic quantum

mechanical milestones.

- Keith Schwab

Aashish Clerk, of McGill University in Montreal, Canada thinks the work will have far-reaching applications. The fragility of quantum states has been a big ob-stacle for building quantum computers. Understanding the quantum-classical crossover could help us learn how to prevent quantum effects from breaking down, says Clerk.

MARKUS ASPELMEYER

Cornell University

Crossing Continents

It’s one thing to share theories and ideas with researchers overseas, but how tough is it to carry out cross-continental experiments? No stranger to international scientific collaboration, Zeilinger has worked with scientists in New York and Boston, while being based in Vienna. He believes the ability to work for the common good, rather than competing, is a simple but essential element.

One frontier not probed

enough is in the

direction towards the

real world.

enough is in the

direction towards the

real world.

- Tony Leggett

Currently, students from Vienna regularly travel to New York to fabricate the nanotools and learn some cooling techniques, while some Cornell students will also begin to travel to Vienna soon to do some measurements. Technologies such as Skype and email also allow the group to stay connected despite being spread across a big area geographically.

"I really think this is the best that could happen when people with very different backgrounds meet and collaborate," said Aspelmeyer. "It’s been great discussing ideas with Keith. Huge fun."

And the fruits of their collaboration will begin to ripen as temperatures continue to drop.

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NARENDRA NATH wrote on December 19, 2009

Mesomorphic region experiments are required to be conducted. It may be a difficult regime but human beings are smart enough to generate new design ideas in the minds of prospective physicists to conduct such experiments in the near future. What about High energy Compton scattering using nanostructured crystal of silver or gold! Where to see the effect of change in value of Planck's constant, compton scattered electron or the scattered photon?

Mesomorphic region experiments are required to be conducted. It may be a difficult regime but human beings are smart enough to generate new design ideas in the minds of prospective physicists to conduct such experiments in the near future. What about High energy Compton scattering using nanostructured crystal of silver or gold! Where to see the effect of change in value of Planck's constant, compton scattered electron or the scattered photon?

TEJINDER SINGH wrote on November 28, 2009

The paper

http://arxiv.org/abs/0711.3773

argues that quantum theory is intrinsically nonlinear, and goes to the standard linear limit for microscopic objects. THe nonlinear theory goes to the classical limit for large objects, but departs from linear quantum mechanics for mesoscopic objects.

Because of the nnlinearity, the lifetime of two superposed states is no longer infinite. It decreases as the number of atoms in the object under study increases, going from an...

The paper

http://arxiv.org/abs/0711.3773

argues that quantum theory is intrinsically nonlinear, and goes to the standard linear limit for microscopic objects. THe nonlinear theory goes to the classical limit for large objects, but departs from linear quantum mechanics for mesoscopic objects.

Because of the nnlinearity, the lifetime of two superposed states is no longer infinite. It decreases as the number of atoms in the object under study increases, going from an...

NARENDRA NATH wrote on November 7, 2009

This bold attempt at a tough problem is highly commendable. My personal interest has arisen in this experiment from the desire to test the valdity of possible variation in the value of h above 0 limit for classical objetcs/processes. The interst follows an attempt by Tejinger Singh of TIFR, Mumbai, India who has developed a theory for such a mesomorphic region where neither classical nor quantum mechanics is strictly valid.

I have yet to grasp the full import of the planning being done by...

This bold attempt at a tough problem is highly commendable. My personal interest has arisen in this experiment from the desire to test the valdity of possible variation in the value of h above 0 limit for classical objetcs/processes. The interst follows an attempt by Tejinger Singh of TIFR, Mumbai, India who has developed a theory for such a mesomorphic region where neither classical nor quantum mechanics is strictly valid.

I have yet to grasp the full import of the planning being done by...

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