Proposed Quantum Computer Consists of Billions of Electron Spins

Sep 09, 2009 By Lisa Zyga feature
The physical setup of the quantum computer consists of a superconducting transmission line cavity coupled to an ensemble of electron spins and a transmon Cooper pair box. The cavity dimensions allow 100 billion electron spins to be coupled to the cavity mode, which could be used to make hundreds of physical qubits. Image copyright: J.H. Wesenberg, et al.

(PhysOrg.com) -- While researchers have already demonstrated the building blocks for few-bit quantum computers, scaling these systems up to large quantum computers remains a challenge. One of the biggest problems is developing physical systems that can reliably store thousands of qubits, and enabling bits and pairs to be addressed individually for gate operations.

With this issue in mind, scientists have recently proposed a scheme that uses an ensemble of about 100 billion electron spins. They show that hundreds of physical qubits can be made from these collective excitations. The researchers, Janus Wesenberg from the University of Oxford, and coauthors from Oxford, Yale University and the University of Aarhus in Denmark, have published the proposed system in a recent issue of .

The system can also perform qubit encoding and provide one- and two-bit gates for quantum computing. In the setup, the electron spins are coupled to a superconducting transmission line cavity. In turn, this cavity is coupled to a transmon Cooper pair box that carries out the gate operations.

“A single electron spin only interacts very weakly with its environment: this makes it a good , except that it is very hard to initialize or read out,” Wesenberg explained to PhysOrg.com. “In the ensemble register we make use of the fact that the collective interaction between an ensemble of billions of spins and a microwave cavity is greatly enhanced by the so-called superradiant effect. This makes it possible to transfer a microwave photon (carrying a qubit), from the cavity to the spin ensemble in a few tens of nanoseconds compared to a significant fraction of a second for a single spin. Once the photon has been transferred to the ensemble, it lives as an delocalized excitation.

“The state of the system is a quantum superposition of each spin being excited, that is, flipped relative to the very strong that has been applied to the system. There is an infinite number of ways in which a single excitation can be superpositioned in this way, and these can be described in terms of spin waves. By applying a magnetic gradient pulse, we can transfer an excitation that lives as one kind of spin wave to another kind of spin wave.”

As Wesenberg added, the study brings up two independent new ideas.

“Firstly, there is the idea to couple an ensemble of electron spins to a stripline resonator,” he said. “While this is a novel idea, it is a straightforward extension of previous work (by Peter Zoller and many others), on coupling ensembles of polar molecules, Rydberg atoms etc. to such stripline cavities. The main advantage of using electron spins is that they can simply be smeared onto the stripline substrate without any need for complex trapping arrangements. Secondly, there is the idea of using the holographic principle to address a large number of modes in the ensemble by means of a controllable magnetic gradient. This is a relatively straightforward extension of work by one of the authors (K. Mølmer), on holographic storage.”

As the scientists explain in their study, one of the advantages of this setup is that a large number of spins can be controlled without requiring single spin measurement. Depending on the materials used, the system could achieve spin coherence times of up to tens of milliseconds, which could be used to build a solid-state device.

“The immediate plan is to demonstrate experimentally that this works,” Wesenberg said. “First in the semi-classical setting (which is essentially electron spin resonance spectroscopy), and later in the quantum regime. Experiments to this end are underway at Yale and Oxford.”

More information: J.H. Wesenberg, et al. “ with an Electron Spin Ensemble.” Physical Review Letters 103, 070502 (2009). DOI: 10.1103/PhysRevLett.103.070502

Copyright 2009 PhysOrg.com.
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User comments : 23

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Adriab
2.3 / 5 (3) Sep 09, 2009
Ok, this idea sounds like a good approach, but not for a PC sort of computer yet. If I had to guess a quantum computer will first appear in a Mainframe sort of role. These things will be hard to produce and run, just think about those super-conductors.

Although, a company like google probably could afford one or two, and they most likely already have the algorithms figured out to make better searches and the like.
earls
3.5 / 5 (4) Sep 09, 2009
I remember the day, sonny, when quantum computers were as big as a house!! They only had billions of electron spins! Everyone thought "that ought to be enough for everyone!"
danman5000
3 / 5 (4) Sep 09, 2009
Whatever you say, Gramps. I'm gonna take the hover car over to Electro-Donald's for a synthburger.
AlIIII
2.3 / 5 (3) Sep 09, 2009
Let's be civil!
Adriab
2.7 / 5 (3) Sep 09, 2009
mmm, synthburgers...
thales
1.8 / 5 (4) Sep 09, 2009
I personally think that when the first game of Q*bert is played on a qubit based computer, the universe will implode.
Mr_Man
2.3 / 5 (3) Sep 09, 2009
I can see the signs at Best Buy now..



"HP Pavilion 2-bit quantum processor w/ 1 billion trillion electrons"

The "cycles per second" race will be replaced by a "number of electrons" race.

...That might have been funnier a few years ago when there was still a "cycles per second" race with CPUs..
poi
2.7 / 5 (3) Sep 09, 2009
As the scientists explain in their study, one of the advantages of this setup is that a large number of spins can be controlled without requiring single spin measurement. Depending on the materials used, the system could achieve spin coherence times of up to tens of milliseconds, which could be used to build a solid-state device.

Good job!
Seems to be the right direction to take.
The goal then would be to reduce the number of electron spins in the array to make it smaller and smaller until we reach the single electron spin measurement.
Good luck!
dirk_bruere
3 / 5 (4) Sep 09, 2009
Nobody will ever need more than 640,000 Qbits
MorituriMax
3 / 5 (2) Sep 09, 2009
@dirk bruere

Gatist!
Ethelred
2.6 / 5 (5) Sep 10, 2009
If anyone is curious the humorless gutless ONE rater is
nanotech_republika_pl. Who has made a staggering TWO posts in TWO years. Both this month.

Heck even AlIIII was at least a bit funny.

Ethelred

Death to short posts. Tell Physorg what you think.
Hry b4 al psts luk lik ts
nuge
1.5 / 5 (2) Sep 10, 2009
hundreds of cubits? holy shit, isn't that equivalent to 2^100 ordinary bits?
SmartK8
3 / 5 (3) Sep 10, 2009
While I'm really getting lost on the technology of those quantum computers, I find it very exciting anyway. I guess, I won't be able to put together the next-gen computers at home anymore. Maybe I won't even be able to look at the internals, as it may compromise the quantum states inside.

Ethelred: I was wondering about that. Maybe physorg should consider putting an initial rating of the comments to 3.0 (meaning neutral), thus making 1.0 and 5.0 the limits, that can only ever be approximated. Rather than this system allowing for one voter to throw the meaningless ones (or any other rank in that matter).
Ethelred
3.7 / 5 (3) Sep 10, 2009
holy shit, isn't that equivalent to 2^100 ordinary bits?

Right. Whats a cubit. - Bill Cosby as Moses.

http://en.wikiped...ki/Qubit
A qubit has some similarities to a classical bit, but is overall very different. Like a bit, a qubit can have two possible values—normally a 0 or a 1. The difference is that whereas a bit must be either 0 or 1, a qubit can be 0, 1, or a superposition of both.

To some extent it depends on what you use them for, I think. Mostly it would be something between 2^8 and 2^9. Good for breaking AES 256 up to WHATEVERCRYPT 999. So use more than 1000 bits for your encryption and you are safe.

Qubits are not going to be used for information storage, at least at the beginning. They will be used much as Registers are used in standard computers. A place where numbers, or rather bits, are manipulated.

Ethelred

Death to short posts. Tell Physorg what you think.
Hry b4 al psts luk lik ts
Adriab
3 / 5 (2) Sep 10, 2009
[Q]To some extent it depends on what you use them for, I think. Mostly it would be something between 2^8 and 2^9. Good for breaking AES 256 up to WHATEVERCRYPT 999. So use more than 1000 bits for your encryption and you are safe.[/Q]

Shoots anything like RSA that is based on difficulty (or at least slowness) of factorization all to hell too.
Ethelred
3.4 / 5 (5) Sep 10, 2009
Maybe physorg should consider putting an initial rating of the comments to 3.0 (meaning neutral), thus making 1.0 and 5.0 the limits, that can only ever be approximated.


That seems better than what we have. Personally I am all for throwing the rating system out the window. If nothing else it would get rid of some of the sock puppets that exist only to rate people without fear of a well earned reprisal.

Ethelred

Death to short posts. Tell Physorg what you think.
Hry b4 al psts luk lik ts

See bottom of page for links like CONTACT US. Who knows maybe someone will read the feedback. Or at least pass it through a Qubit register and parse the total bit mass of fury. Not to be confused with furry.
CynthiaY29
2.5 / 5 (4) Sep 10, 2009
I can just hear the tech support call now, "I didn't mean to let all my electrons escape, how do I get them back?" Call a physicist. =D
sender
1 / 5 (1) Sep 10, 2009
i would think variable non-blinking bi-stable semiconductors would be more efficient and power saving when manipulating routines in comparison to single electron spins
Birger
3 / 5 (2) Sep 10, 2009
Since pattern recognition uses up a lot of computing power, maybe this would be a good early application for quantum computers? The human mind uses many layers of neural networks for this task, but compute software can not (yet) scale up neural networks...
If smart mines and AA missiles had quantum computers to filter images through pattern recognition software, they would be able to ignore decoys, and invading armies and bombers would be at a disadvantage.
E_L_Earnhardt
1 / 5 (1) Sep 10, 2009
COMPARE YOUR WORK TO "LIVING CELL" CREATION AND OPERATION! INCLUDE HYDROTHERMIC MANIPULATION AND YOU CAN EXPLAIN, AT LAST, ITS FUNCTION AND MALFUNCTION! IT'S AN ELECTRON SPIN DEVICE!!!
Ricochet
3.3 / 5 (4) Sep 10, 2009
COMPARE YOUR WORK TO "LIVING CELL" CREATION AND OPERATION! INCLUDE HYDROTHERMIC MANIPULATION AND YOU CAN EXPLAIN, AT LAST, ITS FUNCTION AND MALFUNCTION! IT'S AN ELECTRON SPIN DEVICE!!!


Please stop yelling. It gives me a headache.
otto1923
not rated yet Sep 12, 2009
They only had billions of electron spins! Everyone thought "that ought to be enough for everyone!"
And I remember when everybody thought they could actually think, then along came thinking machines and proved them wrong.
otto1923
5 / 5 (3) Sep 12, 2009
That seems better than what we have. Personally I am all for throwing the rating system out the window.
I think the govt should fund a study to find out what makes humorless star nazis tick. An invaluable source of knowledge which should be investigated. For Posterity. Whatever that is-

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