Physicists move one step closer to quantum computer

Oct 04, 2011
In his quest to create a "topological insulator," Rice graduate student Ivan Knez spent hundreds of hours modifying tiny pieces of semiconductors in Rice University's clean room. Credit: Jeff Fitlow/Rice University

Rice University physicists have created a tiny "electron superhighway" that could one day be useful for building a quantum computer, a new type of computer that will use quantum particles in place of the digital transistors found in today's microchips.

In a recent paper in , Rice physicists Rui-Rui Du and Ivan Knez describe a new method for making a tiny device called a "quantum spin Hall topological insulator." The device, which acts as an electron superhighway, is one of the building blocks needed to create quantum particles that store and manipulate data.

Today's computers use binary bits of data that are either ones or zeros. Quantum computers would use , or "," which can be both ones and zeros at the same time, thanks to the quirks of .

This quirk gives quantum computers a huge edge in performing particular types of calculations, said Du, professor of physics and astronomy at Rice. For example, intense computing tasks like code-breaking, climate modeling and biomedical simulation could be completed thousands of times faster with quantum computers.

"In principle, we don't need many qubits to create a ," he said. "In terms of information density, a silicon microprocessor with 1 billion transistors would be roughly equal to a quantum processor with 30 qubits."

In the race to build quantum computers, researchers are taking a number of approaches to creating qubits. Regardless of the approach, a common problem is making certain that information encoded into qubits isn't lost over time due to . This is known as "."

This semiconductor chip contains hundreds of tiny "electron superhighways," submicroscopic devices that could one day be useful for building quantum computers. Credit: Jeff Fitlow/Rice University

The approach Du and Knez are following is called "topological ." Topological designs are expected to be more fault-tolerant than other types of quantum computers because each qubit in a topological quantum computer will be made from a pair of that have a virtually immutable shared identity. The catch to the topological approach is that physicists have yet to create or observe one of these stable pairs of particles, which are called "Majorana fermions" (pronounced MAH-yor-ah-na FUR-mee-ons).

The elusive Majorana fermions were first proposed in 1937, although the race to create them in a chip has just begun. In particular, physicists believe the particles can be made by marrying a two-dimensional topological insulator -- like the one created by Du and Knez -- to a superconductor.

Topological insulators are oddities; although electricity cannot flow through them, it can flow around their narrow outer edges. If a small square of a topological insulator is attached to a superconductor, Knez said, the elusive Majorana fermions are expected to appear precisely where the materials meet. If this proves true, the devices could potentially be used to generate qubits for quantum computing, he said.

Knez spent more than a year refining the techniques to create Rice's topological insulator. The device is made from a commercial-grade semiconductor that's commonly used in making night-vision goggles. Du said it is the first 2-D topological insulator made from a material that physicists already know how to attach to a superconductor.

"We are well-positioned for the next step," Du said. "Meanwhile, only experiments can tell whether we can find Majorana fermions and whether they are good candidates for creating stable qubits."

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hyongx
5 / 5 (1) Oct 04, 2011
super cool. nanoscale MSE physics for quantum computing.
El_Nose
1 / 5 (1) Oct 04, 2011
could someone explain something --

1 billion transstors = 30 qubits

I guess i always assumed that the superposition would be equivalent to 3 not 6 --- what i am saying is
1 normal bit has 2 state on and off
i thought
1 qubit had 3 states on,off,in between
thus a bit has 2^1 possibilities
while a qubit would have 3^1 possibilities

so 8 normal bits is 2^8 = 2^1 * 2^1 * 2^1 ... = 256
and 8 quibits is 3^8 = 6561

so i figured that 1 billion transistors would be the equation
1000000000 = 3^x where x =
log( 1000000000) / log (3) = ~19 or 3^19 is just over 1 B
but 30 implies one of two equations

1) 1000000000 = x^30 ( most reasonable in my opinion )
but if you are a CS major you don't even need to do the math to know x = 2 == 2^30 = i GB

2) 1000000000 = 30^x ( ridiculous in my eyes )
but hear log (1000000000) / log (30) = 6.09

So which is it ???
MattChristensen
5 / 5 (1) Oct 04, 2011
El Nose, A qubit is not 3^1. It is a superposition of off and on states. A bit is either 1> or 0>, a qubit is a*1> b*0> where both a and b are variables between 0 and 1. I'm not sure where the author gets a billion from, but this explanation of qubits is correct.
marcin_szczurowski
5 / 5 (1) Oct 04, 2011
Yep, qbit has a continuum of possible configurations. We shouldn't quantitize qubit states... Wait, what? :D
El_Nose
not rated yet Oct 04, 2011
I am sorry for not being clear -- if you need 30 qubits to represent 1 billion then there is no difference between this qubit and a normal bit -- because it only takes 30 bits to represent 1 billion

-- i hope that is more clear
mekraab
2 / 5 (1) Oct 04, 2011
"one step closer"? Dwave sold its first quantum computer to lockheed-martin in may, doesn't that make us there not closer?
CHollman82
1.7 / 5 (6) Oct 04, 2011
I always thought a qubit could represent any value between 0 and 1... meaning each one could represent the full range of possible values assuming infinite resolution (which may not be a good assumption)... which means each one could represent an entire file of any arbitrary size...
CHollman82
2 / 5 (8) Oct 04, 2011
A single qubit could store an entire bluray movie, for example... because all that a bluray movie is, in it's digital representation, is one very large number, which could just as easily be expressed as a fractional value between 0 and 1.

What I mean is, assume the bit pattern of a file, any file, comes up to equal the number 3452526252510145607... It's completely trivial to slap a zero and a decimal point in front of that number in order to represent it as a value between 0 and 1: 0.3452526252510145607.

Of course a bluray movie would have to represented by a number with billions of digits, but you get the idea.

However, I highly doubt there is infinite resolution to quantum superposition and I KNOW we will never be able to measure accurately enough to use such high resolution.
CHollman82
2.3 / 5 (8) Oct 04, 2011
This brings up an interesting point that few people understand but are amazed by when I explain it to them... most people realize that files on a computer, be it a program or a text document or a movie, consist solely of numbers... but did you know that each file on your computer could be represented by a SINGLE number?

Each movie file, each PDF e-book, each application, each MP3 music file, etc are simply numbers, each one is only ONE number. Granted the number is a very large one for files of any significance.
CHollman82
1 / 5 (3) Oct 04, 2011
Understanding this, you should realize that you can literally enumerate all possible movies of a given length, or all possible images of a given resolution, or all possible songs of a given bitrate and length... very simply, just by counting.
CHollman82
1 / 5 (3) Oct 04, 2011
Now you should be able to reach the conclusion that the bit pattern on your ENTIRE hard drive could be represented by a single number as well, therefore a single qubit of infinite resolution could represent your ENTIRE 2 terabyte hard drive (or 1000 terabyte hard drive, or million terabyte hard drive, it doesn't matter).

Theoretically, assuming quantum superposition is of infinite resolution, a single qubit could represent all of the data in the world... unfortunately we'll never be able to measure that
El_Nose
5 / 5 (2) Oct 04, 2011
hey CHoll -- the second you attempt to read that qubit it will collapse into a distinct value
CHollman82
1 / 5 (3) Oct 04, 2011
hey CHoll -- the second you attempt to read that qubit it will collapse into a distinct value


Of only 2 potential values? Or how many?
El_Nose
not rated yet Oct 04, 2011
depends on the enganlement parameter... spin has to be an integer i believe -- maybe half integers
Callippo
1 / 5 (1) Oct 04, 2011
How the Majorana fermions differ from Cooper pairs?
Nanobanano
1 / 5 (1) Oct 04, 2011
ElNose:

There are two issues here.

1) Superposition should allow several neat tricks in changing base for storage, as opposed to calculation. So if you had a non-volatile quantum memory, you are correct that you could interpret the superimposed state as a "base 3" switch.

2) Superposition allows a quantum computer to solve certain classes of problems much faster than an ordinary computer, for example, who wins a game (such as chess).

The quantum computer can solve that in fewer steps than a classical computer, therefore it needs fewer memory locations to store data and functions. In classical comptuers, the memory locations and function names become so complicated that much of memory is stimply storing the addresses of other memory locations...

3) Quantum computers can solve some classes of problems that electronic computer can never solve at all. For example, generate a random integer from 1 to 3 without a "catch" for the 4 that a classical computer would make...
Nanobanano
1 / 5 (1) Oct 04, 2011
3) continued...

In a classical computer, if you want to generate a random integer from 1 to 3, you have to generate a random number from 0 to 3, and then if you got a 0, re-do the random number generator until you get a number other than 0. OR use some other random float generator and then "scale" it to integers from 1 to 3.

Either way you end up wasting steps.

That's just a very easy to see example of a classical problem that a quantum computer could do better.

There are also quantum algorithms that cannot be solved at all by a classical computer, and which may have practical applications in like medicine and materials sciences, and perhaps weather modeling or cosmology or spac eprograms or even A.I. It just depends on what the engineers can convert from "theory and formula" to a practical device or application once the first quantum computers are made....
ForFreeMinds
2 / 5 (4) Oct 04, 2011
Given all the "one step closer to quantum computing" stories, it appears there are thousands of steps needed, and who knows how long it will be before one is built. Then how much longer before their are commercially viable?
Deesky
4.3 / 5 (11) Oct 04, 2011
A single qubit could store an entire bluray movie, for example... because all that a bluray movie is, in it's digital representation, is one very large number, which could just as easily be expressed as a fractional value between 0 and 1.

This isn't the case. A single qubit cannot store an infinite number of states between 0 & 1. A single qubit can be used to represent only two states, 0 & 1, but do so simultaneously (unlike a classical bit which is either 0 or 1).

The power of qubits comes from this superposition of dual states. Eg, 3 normal bits can only represent a single number, whereas 3 qubits can represent 8 numbers at the SAME time (2^3). 10 qubits -> 2^10 = 1024 simultaneous numbers, etc.

But despite this power, qubits aren't much more useful than normal bits for data storage due to decoherence - when observed, they collapse to a single RANDOM number.

The power of a quantum computer lies in its massively parallel computational nature, not in data storage.
bluehigh
1.5 / 5 (8) Oct 05, 2011
Crikey, a lovers tiff.

CHollman correctly assumes that a qubit can contain any value.

Deesky gets hot and bothered because when he observes the data it vanishes.

CHollman starts counting to find some romantic new music to please his lover, while monkeys with typewriters watch.

Deesky names the new tune decoherence in an attempt to baffle others because he believes that a qubit contains all the music in the universe simultaneously but he just can't listen to it ever. 'It all sounds like random noise' he/she shrieks.

Annoyed, nanobanano spouts general mumbo jumbo without any specific practical implementations and decides a threesome is out of the question tonight.

Such unseemly behavior!

The catch to the topological approach is that physicists have yet to create or observe one of these stable pairs of particles,
- from the article

So, they don't exist? Oh thats right, just another model from the guys in a money shower. Whats to discuss? Hypothetical Hypotheticals.
CHollman82
3 / 5 (6) Oct 05, 2011
Nano you realize that what you said about random number generation is nonsense right? As is most of what you write most of the time...

CHollman82
1.8 / 5 (5) Oct 05, 2011
Hey Megadeath, can I ask why you gave me a bunch of ones? I clearly prefaced my explanation with the fact that it is based on the ASSUMPTION that quantum superposition has infinite many "states"...

Furthermore, everything else I said about a single number being able to represent any file or any collection of files is correct...
bluehigh
1 / 5 (2) Oct 05, 2011
CHollman, you are clearly a bright guy. Stop tilting at windmills. Some battles are not worth fighting.
Ryan1981
not rated yet Oct 07, 2011
@CHollman, if you have not done so already, you should watch the SF movie PI