Many of the trapped-ion experiments at NIST have involved shuttling ions through a multizone linear trap. Extending this idea to much larger systems, however, will require more sophisticated structures with a multitude of electrodes that could guide the ions in any direction. The electrodes would have to be very small—in the range of 10 to 100 millionths of a meter—to confine and control the ion-shuttling procedure precisely. Fortunately, the builders of trapped-ion quantum computers can take advantage of microfabrication techniques, such as microelectromechanical systems (MEMS) and semiconductor lithography, that are already used to construct conventional computer chips.
Over the past year several research groups have demonstrated the first integrated ion traps. Scientists at the University of Michigan and the Laboratory for Physical Sciences at the University of Maryland employed a gallium arsenide semiconductor structure for their quantum chip. Investigators at NIST developed a new ion-trap geometry in which the ions float above a chip’s surface. Groups at Alcatel-Lucent and Sandia National Laboratories have fabricated even fancier ion traps on silicon chips. Much work remains to be done on these chip traps. The atomic noise emanating from nearby surfaces must be reduced, perhaps by cooling the electrodes with liquid nitrogen or liquid helium. And researchers must skillfully choreograph the movement of ions across the chip to avoid heating the particles and disturbing their positions. For example, the shuttling of ions around a simple corner in a T junction requires the careful synchronization of electric forces.
The Photon Connection
Meanwhile other scientists are pursuing an alternative way to build quantum computers from trapped ions, and this approach may circumvent some of the difficulties in controlling the motion of the ions. Instead of coupling the ions through their oscillatory motions, these researchers are using photons to link the qubits. In a scheme based on ideas described in 2001 by Cirac, Zoller and their colleagues Luming Duan of the University of Michigan and Mikhail Lukin of Harvard University, photons are emitted from each trapped ion so that the attributes of the photons—such as polarization or color—become entangled with the internal, magnetic qubit states of the ion emitter. The photons then travel down optical fibers to a beam splitter, a device typically used to split a light beam in two. In this setup, however, the beam splitter works in reverse: the photons approach the device from opposite sides, and if the particles have the same polarization and color, they interfere with each other and can emerge only along the same path. But if the photons have different polarizations or colors—indicating that the trapped ions are in different qubit states—the particles can follow separate paths to a pair of detectors. The important point here is that after the photons are detected, it is not possible to tell which ion has emitted which photon, and this quantum phenomenon produces entanglement between the ions.
The emitted photons, though, are not successfully collected or detected in every attempt. In fact, the vast majority of the time the photons are lost and the ions are not entangled. But it is still possible to recover from this type of error by repeating the process and simply waiting for photons to be simultaneously counted on the detectors. Once this occurs, even though the ions may be widely separated, the manipulation of one of the qubits will affect the other, allowing the construction of a CNOT logic gate.
Scientists at the University of Michigan and the University of Maryland have successfully entangled two trapped-ion qubits, separated by about one meter, using the interference of their emitted photons. The main obstacle in such experiments is the low rate of entanglement generation; the likelihood of capturing these single photons into a fiber is so small that ions are entangled only a few times per minute. That rate could be increased dramatically by surrounding each ion with highly reflective mirrors in a so-called optical cavity, which would greatly improve the coupling of the ion emission with the optical fibers, but this enhancement is currently very difficult to accomplish experimentally. Nevertheless, as long as the interference eventually occurs, researchers can still use the system for quantum information processing. (The procedure is comparable to getting cable TV installed in a new house: although it may take many phone calls to get the service provider to install the system, eventually the cable is hooked up, and you can watch TV.)
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19 Comments
Add CommentI^mz .... I = infinite ^ angle of mz = largest and smalles measurement programmed ga programming
Reply | Report Abuse | Link to thisIs the editor on vacation?
Reply | Report Abuse | Link to thisThis article starts minus the capital letter.
"...technological advances have dramatically boosted the..." Is that the beginning of the sentence? If so, why isn't the 't' capitalized??
Are we just throwing out the basic grammar rule book now? Shame on Sci Am. Don't publish if you aren't doing to do it right.
Quasimodo-Were you picked on a lot as a kid? The article is concise and informative. Get over yourself and take the benefit from this article that it most definitely offers. Besides I do not know what article you read but the capitalization and punctuation is fine. The sentence starts:
Reply | Report Abuse | Link to this"Over the past several decades technological advances have dramatically boosted the speed and reliability of computers."
So you have made an even bigger fool of yourself than I first assumed.
**The field of quantum information science promises to radically change the rules of computing.** As scientists still work on small size quantum gates, they cannot afford arguing about new computing rules at present. Designing the new rules simply belongs to another realm of understanding. Similarly, what evolutionism could prove so far is so inexistent that its early allegations about origin of life are boldly presumptuous. So far, origin of life is not a scientific debate.
Reply | Report Abuse | Link to thisSciMike,
Reply | Report Abuse | Link to thisProfessionals write professionally, got it? Too bad if you don't. You answered my question with a question. That's pretty unprofessional.
Either answer my question, or hush up. My question had Nothing to do with the actual facts put forth in the body of the article. Grow up and smell the decade.
I have a question, if anyone here can help me out on this. Considering qubits that are based on the magnetic orientation of a trapped ion, as I understand it, in order to make a particle (say a proton) "flip" in a magnetic field from one orientation to another, we need to apply an amount of energy (by using a wave of particular frequency) that is exactly equivalent to the energy gap between the two spin states (orientations). So, how exactly is it possible to make the particle be in the superposition state? Do we apply half the energy or twice as much (which doesn't make sense), or what exactly do we do? I guess this is the whole point of quantum mechanics...but I dont really get it.
Reply | Report Abuse | Link to thisOh yeah, and something else regarding logic gates....maybe I misunderstood, but how is it possible to form classic logic gates like AND and OR gates using qubits? I mean, these gates are based on determinable deductive logic, but in quantum mechanics, there is always uncertainty (heisenberg's principle) and logic is based on probability (am I right?), so how is that possible?
Reply | Report Abuse | Link to thisIt is of certain intrigue how the evolutionary procedure of this technological branch would reach the ironic imminence of its possible outcomes, which will set forward a whole new perspective on the computational processes within modern electronics. But considering the constant repression the elite has over the introduction of ideas that can potentially compromise their agenda, this technology would still be far from reaching consumer applications.
Reply | Report Abuse | Link to thisOh yeah, and something else regarding logic gates....maybe I misunderstood, but how is it possible to form classic logic gates like AND and OR gates using qubits? I mean, these gates are based on determinable deductive logic, but in quantum mechanics, there is always uncertainty (heisenberg's principle) and logic is based on probability (am I right?), so how is that possible?
Reply | Report Abuse | Link to thisQuantum dot: Are you trying to understand how the gates work or are you just asking how classical gates can be used at all? If you are asking how a classical logic gate works in this situation I will explain that. The logic behind the gates (as I see it) works on a basic principle of quantum mechanics: when you measure something, it changes. Uncertainty doesn't apply in this instance. I see this as a similarity to the double slit experiment where a physical medium is used to measure a quantum state, which forces it to choose and orientation.
ID-based COMPLEX GATES : ID global approach holds the overall answer (God), to be verified in subsequent details. Conversely, evolutionism starts from details (fossils), with no serious intention of reaching a significant answer(Void). Similarly, quantum gates computing rules are determined from software design, while Hardware approach deals with details void of meaning. For instance, the elementary quantum gate described here may get two meanings: CNOT (already described) and XOR. Let us call D1, D2 respectively the first and second data of the gate and A the XOR result. If D1 is 1 and D2 is 1, D2 holds the result as 0: A=D2=0**D1=1, D2=0: A=D2=1** D1=0, D2=1: A=D2=1 **D1=0, D2=0: A=D2=0 ** It is therefore software level interpretation (as XOR or CNOT) that gives the gate its actual meaning, hardware approach simply describing the gate maravellous potential.
Reply | Report Abuse | Link to thisQuasimodo , I find it hilarious that your incorrect rant about an error in their article, is followed with this statement by you:
Reply | Report Abuse | Link to this"Shame on Sci Am. Don't publish if you aren't doing to do it right. "
Hilarious! Shame on you, don't comment if you aren't going to do it correctly!
Kevino819, thank you for your response. You mentioned the basic quantum mechanical principle of: when we measure something, it changes, but what I was trying to say is I just don't understand how its possible to run an algorithm or a program, or to program the logic gates themselves, when the outcome is unknown and based on the measurement, there is no expected result, do you see what I'm trying to say? I mean, its like trying to use logic gates for something where there is no logic.
Reply | Report Abuse | Link to thisWith the AND and OR gates, you'd do it kinda like it's done like it's done in a normal computer. AND: measure two qubits. if they're both in the 1 state, then your AND thing gets a 1 as a return. for the OR gate you'd do the same thing but return a 1 if either qubit was a 1.
Reply | Report Abuse | Link to thisOh, and i think that the qubits can use any of their properties as the data carrying ones, it doesn't have to be their magnetic alignment, it can be anything.
Something that would be very cool about this technology (if i'm assuming correctly) is that you could entangle particals and seperate them between a pair of machines, creating a wireless connection between the two of infinite range. It would work in a tunnel, underground, on the moon! Or, you could go a stage further and link all the processors of all Quantum computers in the world so that they share their computing power amongst all the users!
I will be the first one implements commercial Qcomputer
Reply | Report Abuse | Link to thisI will be the first one implements commercial Qcomputer.
Reply | Report Abuse | Link to thisIt is a very nice thing to see your excellent work and I like your article very much. With your rich knowledge, we can learn more from your wonderful post. Thanks so much.
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What's most interesting is how conditional programs might be able to use probabilistic results of conditional tests - will this be accomplished through probabilistic branch functions? 'If taxable income >72% Then 48% Perform tax calculation...'
Reply | Report Abuse | Link to thisQuasi, SciMike was right. You were and are wrong. And, oddly, you persisted in being wrong.
Reply | Report Abuse | Link to thisI have been puzzled of late. With the Higgs Boson "found" does that mean we have M-theory to ponder. I mean the standard model is vindicated and there is a bridge to quantum effects within the standard model. If this is correct the M-theory is valid; please correct me if I have strayed. What I want to know is what does an electron, for instance, look like in any of the other 7 dimensions and can that be computed using this method. Can we develop sensors and emitters to augment our simple four dimensions? Does that form the basis of what dark matter is? This has had me in a transfixed state since the Higgs was defined. If anyone can elucidate more please feel free!
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