Right now the device’s low efficiency limits its usefulness, comments Paul G. Kwiat, a quantum optics expert at the University of Illinois at Urbana-Champaign. But if the team can improve efficiency, he notes, it “could open a new, potentially efficient approach to quantum computing.”

This article was originally published with the title Quantum Light Switch.

10 Comments

1. 1. jtdwyer 11:22 AM 9/8/10

   Is there some physical property of photons that offers inherent advantages over electrons in producing quantum logic circuits? It be disappointing to finally make a photonic computer only to find that it offers no real advantage in miniaturization or resulting speed over electronic computers...

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2. 2. Dimitris 03:59 PM 9/8/10

   Photons travel much faster than electrons, among others.

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3. 3. jtdwyer in reply to Dimitris 04:42 PM 9/8/10

   Dimitris - As I understand, contrary to popular conception, the propagation of an electron through a circuit can approach the 'speed of light' in a vacuum. Also, the speed of light traversing some unspecified optical circuit in an optical device could not attain the 'speed of light' in a vacuum, unless the device utilized a single light source and the entire photon path were within a single vacuum. I think remains to be seen whether a photonic computer would in practice be faster than an electronic computer.

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4. 4. tharriss 07:19 PM 9/8/10

   What about this part though:
   
   "quantum computers could perform certain operations in parallel. In principle, they could quickly perform calculations that a typical computer could not do, at least not before the sun swells up and bakes the earth five billion years from now"
   
   So while the photons might not in the end travel faster, it is possible their other characteristics could make the overall performance faster, or more secure, etc.

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5. 5. Wayne Williamson 07:30 PM 9/8/10

   this article is mixing apples and oranges....
   
   two or more entangle photons could represent a qubit...as near as i can tell they are not talking about entanglement so no qubit....
   
   they are just using one beam(photon) to control another....all by itself a great discovery...although at 20 percent they need several orders of magnitude to make it useable...
   
   

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6. 6. jtdwyer in reply to tharriss 09:43 PM 9/8/10

   tharriss - Good catch; I wasn't really paying that close attention.
   
   Wayne Williamson - Mixing apples, oranges and grapes.
   
   I don't think that optical computing provides any benefit relative to electronic computing regarding parallel computer architectures.
   
   I agree there seems to be no entanglement going on here and don't understand the qubit reference.
   
   I particularly like the prospects for really advanced computing:
   
   "They can exist in two states simultaneously and thereby represent both the 0 and 1 of binary code at the same time."
   
   I always wished I could use parallel processing to increase the uncertainty in my programs, but I never dreamed of parallel entangled quantum uncertain computing...

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7. 7. robert schmidt 09:50 PM 9/8/10

   "which would offer unbreakable data security" From what I understand quantum algorithms do not create unbreakable security but make it so one knows if their message has been intercepted or tampered with. If this is incorrect I would be interested to know precisely how "quantum security" works.

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8. 8. Quinn the Eskimo 10:53 PM 9/8/10

   One of the values of photon transmission as opposed to electron is surge. Photons simple ramp up faster and terminate much faster. Making the switching effect very fast.
   
   Electrons, however, can be "stored" much easier. We already know how to make capacitors.
   
   With light, not so much.
   
   On the other hand, we can "see" light, electrons are much tougher to see. So, for display interfaces it's light. For storage it's electrons.
   
   But all bets are off once we find the Higgs.

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9. 9. jtdwyer in reply to Quinn the Eskimo 01:45 AM 9/9/10

   Quinn the Eskimo - Excellent points.
   
   I don't quite see how a device utilizing photon's switching speed advantage for a single photon emission could produce a device whose switch complexity is comparable to current electronic computers, without electronic components. I probably just lack the vision of the optical visionaries.
   
   If the Higgs is ever found, I'll concede all my objections...

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10. 10. ColdDimSum 07:10 PM 12/1/11

    Ok, it's been a long time but since I just read this article others might as well so I thought I would add a few answers.
    
    Electrons moving around produce electromagnetic noise in their environment which poses many very real difficulties for continued miniaturization. Nearby activity increasingly causes false signals/noise as you shrink the electronic components.
    
    Photons do not interfere with one another directly (see first sentence of the article: "Point two laser beams so that they cross each other, and each goes through as if the other one did not exist"), so that makes them ideal for moving information around in very tiny spaces. Furthermore, it's not known how you would gate electric flow with a single atom, which is being demonstrated here.
    
    As to the question of 'storage', I quote from the article "For example, it could store photons and release them at will".
    
    Electrons do not generally move anywhere near the speed of light but the group velocity is much higher than the individual speed of an electron. When you turn on a switch the light comes on almost instantly but the individual electrons are just barely moving.
    
    What you need to understand is the charge carrier density (you can google it). For a 100 volt, 1 amp DC circuit with 2 mm copper wire an electron would zip around at about 2 meters per DAY. With AC the electrons just jiggle back-and-forth slightly. The tricky electric company is selling you the same few electrons over and over again :) -- technically they are selling you the force to jiggle them back and forth.
    
    Thought Experiment: Why would it take TREMENDOUS energies and very specialized equipment to accelerate electrons to near light speed in a particle accelerator if you could do it by just turning on the toaster?
    
    If electrons were being accelerated with sufficient force to get them anywhere near the speed of light at the flick of your light switch we would be awash in cherenkov radiation.

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