John Hersey
Transferring the state of separated ions could point the way to quantum computing.
In recent years, physicists have devised numerous ways to use the oddities of quantum mechanics to transmit and process information.
Now a team of researchers has announced an important step toward using this quantum information: the ghostly transfer of the quantum state of a single ion to another one a meter away. Since ions can store a quantum state for many seconds, this scheme for "quantum teleportation" could buy enough time for manipulations that allow long-distance communications that are immune to eavesdropping, or for computations that exploit the quantum mechanics to perform blazing fast calculations.
To transfer a little quantum information from one atomic-sized system to another, the two systems must start out in the quantum condition called entanglement. Entangled systems always give corresponding answers, like two coins that, although individually unpredictable, always come up one heads and one tails. Physicists have teleported the state between entangled photons of light, but unfortunately, they can't store the quantum information for very long. Recently, other researchers have teleported the much longer-lived quantum state of individual ions, but only when they were trapped very close together.
To transfer persistent quantum information over longer distances, Chris Monroe and his group at the University of Maryland teamed with Luming Duan at the University of Michigan to trap and cool two individual ytterbium ions.The team encoded quantum information by mixing two states that differ only by the angular momentum of the nucleus. Unlike the "0" or "1" value of a bit in ordinary computing, the researchers can create an arbitrary mixture of the two nuclear states, known as a qubit, by subjecting the ions to microwaves. Once formed, an ion retains this mixture for several seconds--long enough to perform calculations that act on both values simultaneously.
Extending a technique that Monroe's team demonstrated in 2007, the researchers exposed both ions to an ultrashort pulse of light, knocking each to a higher-energy state. Each ion then returned to its original state by emitting a photon. Measuring the color of this photon would have left the ion in one of the two nuclear states. But instead, the researchers just tested whether the two photons were different colors. Since they didn't determine which color came from which ion, seeing this result left the ions in an entangled state that included both possibilities.
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Who are these quantum "scientists" fooling? How do you know you've transfered a state from one particle to another if the quantum property in question has superposed states that cannot be observed? Which of those superposed states was transfered? All you can tell about a quantum property is the probability that it will be in one state or another when measured. So if you are going to transfer anything, it should be the probability, not the state. And how are you going to measure this probability after the transfer?
I fully agree with nonlocality but quantum computing is obviously crackpottery and fraud, in my opinion. It is based on superposition, a condition that cannot be observed by definition. Where is the science in that?
Probability does not necessarily imply superposition, I'm sorry. Superposition is just an interpretation, one that is so devoid of logic that Nobel laureate Schrodinger came up with his cat thought experiment in order to show the high strangeness if not the outright stupidity. Others have tried to explain away the silliness of state superposition by conjuring up even more unscientific nonsense like multiple universes. Please! This is looking more like voodoo and superstition than science. There is an infinitely better explanation for the probabilistic nature of quantum interactions that does not insult one's intelligence. Quantum computing scientists should all be investigated for crackpottery and fraud starting with that believer in time travel, Dr. David Deutsch.
Mapou... Perhaps you just don't understand quantum mechanics very well. It should be obvious to even the most dimwitted individual... who holds a master's degree in Hyperbolic Topology (m-glee)
LOL. Wasn't it Feymann who said that nobody understands QM?
Okay great minds, a layman here and even I can understand that nothing close to teleportation is taking place here. Of the two entangled ions, one must be destroyed before the other ion has 'similar' characteristics. "Yes Bones, we obliterate your body at the quantum level and the state of matter somewhere else turns into something that resembles you. It's perfectly safe."
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This document is part of the “How-To Guide for Most Common Measurements” centralized resource portal. This tutorial provides a detailed guide for measurement and device considerations to take temperature measurements using thermocouples. Get an introduction to thermocouples, which are inexpensive sensing devices widely used with PC-based data acquisition systems. Also review some specific thermocouple examples and learn how thermocouples work and ways to integrate them into a data acquisition measurement system.
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pkassebaum
11 Comments
entangled thoughts
Thanks for breaking this news. I was wondering if you could explain the matter a little more. I was left pretty confused (quantum mech has a tendency to do this to me).
"The researchers turned this back into a teleported version of the original state by manipulating it in one of two ways, depending on which state they measured for the left-hand ion."
Is this to say that they were able to transmit info over the space of a meter in a controlled, intentional manner via quantum entanglement? Or that, after measuring the first ion, they could transmit that info through conventional means to knowingly manipulate the second ion so as to set it into the same state as the first? Or are these two statements the same thing?
Thanks!
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donmon
2 Comments
Re: entangled thoughts
Great question! Let me take some space to elaborate.
The measurement of the first ion does not completely characterize its original quantum state. Before the measurement, it was in a mixture of the nuclear (hyperfine) states, called a superposition. (The quantum state is defined by the relative amounts of the two nuclear states and their relative phase.) The rules of quantum mechanics say that after the measurement finds it, by chance, to be in one of those nuclear states, it stays there. The superposition is destroyed. Thus, there is no way for the researchers to send enough classical information to the other ion to let it be put into the original superposition, because they don't have that information.
However, because of the entanglement, the measurement also changes the second ion, putting it into a particular superposition of its nuclear states, which is closely related to the original quantum state of the first ion. But it is not a teleported version of this original quantum state, yet. It can be turned into a teleported version by a manipulation that I'll describe in a moment. But the exact manipulation that needs to be done is different, depending on which nuclear state the first ion was found in. Thus the complete teleportation requires both the entanglement and the communication of classical information (the results of the first measurement).
What kind of "manipulations" are we talking about? By shining microwaves on the ions, the researchers can controllably change the superposition of nuclear states, without destroying the superposition by measuring it. As it turns out, any combination of two states can be thought of as a point on the surface of a sphere. The north and south poles correspond to the pure states. For a superposition, the latitude and longitude reflect the amount of each pure state and their phase. In this picture, the microwaves cause an overall rotation of the sphere, corresponding to a controlled reallocation between the two pure states.
After the first ion is measured, the second ion is left in one of two superpositions, each of which differs from the original by a 90 degree rotation, but in different directions. The researchers use the result from the first ion to choose the rotation that turns the second ion back into a teleported replica. In addition, they also have to do numerous other controlled rotations during the experiment. In particular, to prove that teleportation was happening, they put the first ion into various superpositions by using rotations of a pure state, and then made repeated measurements on the second ion to show that it received the teleported state.
Although it seems as if something is moving between the distant ions, as far as anyone can tell there is no way to use entanglement or any other aspect of quantum mechanics to transmit information faster than the speed of light.
I hope this helps.
Don Monroe (story author--no relation to the researcher)
Reply
pkassebaum
11 Comments
Re: entangled thoughts
Yes, your extended explanation certainly cleared things up for me, as I hope it did for some other readers. Very interesting! Thank you very much for your insight.
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