Search FQXi


RECENT FORUM POSTS

andrea gonzalez: "Interesting stuff to read. Keep it up. If want to collect free gift card..." in Memory, Causality and...

Ian Durham: "Well, Lorraine, if you insist on seeing it that way, I doubt anything I say..." in Measuring Free Will: Ian...

Joe Fisher: "Dear Dr. Kuhn, Today’s Closer To Truth Facebook page contained this..." in First Things First: The...

Poker Online: "https://www.jakartapoker.net/" in Downward causation:...

Enquire us: "Your Ro system desires regular maintenance to confirm it’s continually in..." in Agency in the Physical...

Enquire us: "Our country lies majorly in the tropical belt with a number of cities and..." in Agency in the Physical...

Dermatologist Jaipur: "Enquireus.com is Free Business Listing, Advertising Sites India, Yellow..." in Ed Witten on the Nature...

Dr Gupta: "If you are looking for a best doctor for your health then you don't need to..." in Bonus Koan: Distant...


RECENT ARTICLES
click titles to read articles

First Things First: The Physics of Causality
Why do we remember the past and not the future? Untangling the connections between cause and effect, choice, and entropy.

Can Time Be Saved From Physics?
Philosophers, physicists and neuroscientists discuss how our sense of time’s flow might arise through our interactions with external stimuli—despite suggestions from Einstein's relativity that our perception of the passage of time is an illusion.

Thermo-Demonics
A devilish new framework of thermodynamics that focuses on how we observe information could help illuminate our understanding of probability and rewrite quantum theory.

Gravity's Residue
An unusual approach to unifying the laws of physics could solve Hawking's black-hole information paradox—and its predicted gravitational "memory effect" could be picked up by LIGO.

Could Mind Forge the Universe?
Objective reality, and the laws of physics themselves, emerge from our observations, according to a new framework that turns what we think of as fundamental on its head.


FQXI ARTICLE
August 23, 2019

Crawling at the Speed of Light
To reveal what happens at the quantum realm—and to aid the quest to build quantum computers—physicists are striving to halt light in its tracks.
by Bob Swarup
November 10, 2010
Bookmark and Share


Hobbling Light
Students at the University of Rochester place obstacles in light’s path.
We live in a frenzied fast-paced world. But for physicists hoping to reveal exactly what happens in the quantum realm, finding ways to slow down is not just a luxury, it’s essential—at least in terms of freezing and storing quantum information. With this in mind, some physicists are now taking on the Herculean task of stopping the universe’s fastest mover: light itself. Their work could help bring quantum computers a step closer to reality.

Einstein famously taught us that the speed of light—in a vacuum, at least—is a constant, and nothing can outrun it. So it may seem like a thankless task to try and halt light. But over 50 research groups around the world now work on controlling and manipulating the speed of light.

Quantum Non-Demolition

The efforts of these groups have direct benefits for studying the foundations of quantum mechanics experimentally—which calls for supreme control over photons, says FQXi member Jeff Tollaksen at Chapman University, California. When physicists measure a photon, they disturb it—"collapsing" it from being in a fuzzy superposition with multiple contradictory properties, into a definite state with set properties.

In theory, having performed this measurement, it should be possible to repeat the same measurements on the same photon again and again and get the same set results. But, in practice, most real measurements carried out in the lab disturb the system too much, preventing physicists from performing multiple measurements on the same photon. But technology that slows down light can be used to produce single photons that can be precisely and repeatedly measured in "quantum non-demolition" experiments, says Tollaksen.

John Howell, an optical physicist at the University of Rochester in New York, and his colleagues, are leading the charge to pause light. Think back to school experiments investigating how light is refracted: A straw appears to be bent when looking at it in a glass of water because the speed of the light is affected when it moves through different materials. Howell’s group, and others, are exploiting this by shooting nanosecond pulses of light through hot gases to slow it down.

This represents a whole new
paradigm for quantum control.
- Lene Hau
By carefully adjusting the interaction between the light pulses and the atoms in the gas, Howell’s group have slowed light pulses down from their usual 300,000 kilometers per second to just 0.2 millimeters per second. That means that light, which at full speed can cover the distance from the Earth to the Sun in less than eight and half minutes, can be reduced to traveling no more than roughly the breadth of a single hair in a second.

"John Howell and his whole group at Rochester are first rate, really exceptional physicists," says Tollaksen.

Tollaksen has a particular interest in Howell’s efforts to improve quantum experimental techniques: He and his colleagues are currently using a $70,000 grant from FQXi to investigate a radical reformulation of quantum mechanics—one that suggests that future effects can influence the past in quantum experiments—and derive testable predictions of the idea. Howell’s group has already independently performed some precise photon experiments that Tollaksen believes support the reformulation. (See “The Destiny of the Universe.”)

Quantum Computing Leap

But Howell has another major motive for trying to persuade light to dally. If quantum computers are ever to make the leap from fantasy to reality, physicists will need to find ways to slow down light so that it can be stored directly, says Howell.

John Howell’s group are first
rate, really exceptional physicists.
- Jeff Tollaksen
Quantum computers, in principle, would outperform standard classical computers by utilizing the full information capacity within quantum particles. In practice, however, they are hard to build. The most efficient way to transport quantum information is to encode it in light, but the problem is how to store and manipulate this quantum information effectively. This is already an issue for current classical data-transmission methods, such as fibre-optic networks, which convert light into electronic signals and then back into light again when required. This back-and-forth conversion rapidly degrades the quality of information, which is far from ideal, says Howell.

Break-neck Speed

The field of slowing light is moving forward at break-neck speed. Lene Hau and colleagues at Harvard University are using Bose-Einstein condensates—dense, ultra-cold clouds of atoms that are locked into the same quantum state—to compress light and bring it to a complete halt. Meanwhile physicist Nir Davidson at the Weizmann Institute in Israel and his colleagues have now managed to store and retrieve images in atoms. The race is now on to push storage times beyond their current limits of a few seconds and turn a nifty quantum trick into something meaningful.

Ifan Hughes, an optical physicist at Durham University, UK, explains that the ultimate prize would be creating a quantum hard drive, in which the information from light could be stored in atoms. "This would be an ideal medium for quantum computing," he says.

Lene Hau, a physicist at Harvard University, speaks for many of these researchers when she says: "This represents a whole new paradigm for quantum control."

Comment on this Article

Please read the important Introduction that governs your participation in this community. Inappropriate language will not be tolerated and posts containing such language will be deleted. Otherwise, this is a free speech Forum and all are welcome!
  • Please enter the text of your post, then click the "Submit New Post" button below. You may also optionally add file attachments below before submitting your edits.

  • HTML tags are not permitted in posts, and will automatically be stripped out. Links to other web sites are permitted. For instructions on how to add links, please read the link help page.

  • You may use superscript (10100) and subscript (A2) using [sup]...[/sup] and [sub]...[/sub] tags.

  • You may use bold (important) and italics (emphasize) using [b]...[/b] and [i]...[/i] tags.

  • You may also include LateX equations into your post.

Insert LaTeX Equation [hide]

LaTeX equations may be displayed in FQXi Forum posts by including them within [equation]...[/equation] tags. You may type your equation directly into your post, or use the LaTeX Equation Preview feature below to see how your equation will render (this is recommended).

For more help on LaTeX, please see the LaTeX Project Home Page.

LaTeX Equation Preview



preview equation
clear equation
insert equation into post at cursor


Your name: (optional)






Recent Comments


DO NOT DELETE THIS POST UNDER PENALTY OF LAW!

THIS POST TO BE DELETED ONLY BY THE CONSUMER!

THIS POSTING HAS EVERYTHING TO DO WITH THE SLOWING OF LIGHT:

SEE ATTACHED THEORY

Hi Everyone,

It's me again.

The below June 19, 2011 post this site referenced a June 15, 2011 posting on Out Of The Darkness & Real-Time Physics, also this same FQXi site.Those posts have since been deleted, and so are repeated here to put into context my June 19th...


For the John Howell group & other experimenters along this line.

When you slow down light, can you conduct at the same time the double slit experiment. I would like to confirm that the "slow" version of light will act as a particle, while the fast version of light, a wave.

CIG Theory (posted on Out Of The Darkness & Real-Time Physics this same FQXi site - see June 15, 2011 posting) suggests that mass becomes spatial when it travels at or near "c" rates. My guess is, that if you...


Ok, I just came across an article that stated that you get two different answers depending on whether you consider the photon as a wave or as a particle.

http://physicsworld.com/cws/article/news/41873

There is a sort of resolution claimed in the article (that both are correct depending on what you are asking) but for me I want to know this

If you have a spaceship in deep space emitting a 1 KW beam in a certain direction (or a laser to make it simple) you get a very very...

read all article comments

Please enter your e-mail address:
Note: Joining the FQXi mailing list does not give you a login account or constitute membership in the organization.