(Phys.org) —A computer science professor at Amherst College who recently devised and conducted experiments to test the speed of a quantum computing system against conventional computing methods will soon be presenting a paper with her verdict: quantum computing is, "in some cases, really, really fast."

"Ours is the first paper to my knowledge that compares the quantum approach to conventional methods using the same set of problems," says Catherine McGeoch, the Beitzel Professor in Technology and Society (Computer Science) at Amherst. "I'm not claiming that this is the last word, but it's a first word, a start in trying to sort out what it can do and can't do."

The quantum computer system she was testing, produced by D-Wave just outside Vancouver, BC, has a thumbnail-sized chip that is stored in a dilution refrigerator within a shielded cabinet at near absolute zero, or .02 degrees Kelvin in order to perform its calculations. Whereas conventional computing is binary, 1s and 0s get mashed up in quantum computing, and within that super-cooled (and non-observable) state of flux, a lightning-quick logic takes place, capable of solving problems thousands of times faster than conventional computing methods can, according to her findings.

"You think you're in Dr. Seuss land," McGeoch says. "It's such a whole different approach to computation that you have to wrap your head around this new way of doing things in order to decide how to evaluate it. It's like comparing apples and oranges, or apples and fish, and the difficulty was coming up with experiments and analyses that allowed you to say you'd compared things properly. It definitely was the oddest set of problems I've ever coped with."

McGeoch, author of A Guide to Experimental Algorithmics (Cambridge University Press, 2012), has 25 years of experience setting up experiments to test various facets of computing speed, and is one of the founders of "experimental algorithmics," which she jokingly calls an "oddball niche" of computer science. Her specialty is, however, proving increasingly helpful in trying to evaluate different types of computing performance.

That's why she spent a month last fall at D-Wave, which has produced what it claims is the world's first commercially available quantum computing system. Geordie Rose, D-Wave's founder and Chief Technical Officer, retained McGeoch as an outside consultant to help devise experiments that would test its machines against conventional computers and algorithms.

McGeoch will present her analysis at the peer-reviewed 2013 Association for Computing Machinery (ACM) International Conference on Computing Frontiers in Ischia, Italy, on May 15. Her 10-page-paper, titled "Experimental Evaluation of an Adiabiatic Quantum System for Combinatorial Optimization," was co-authored with Cong Wang, a graduate student at Simon Fraser University.

McGeoch says the calculations the D-Wave excels at involve a specific combinatorial optimization problem, comparable in difficulty to the more famous "travelling salesperson" problem that's been a foundation of theoretical computing for decades.

Briefly stated, the travelling salesperson problem asks this question: Given a list of cities and the distances between each pair of cities, what is the shortest possible route that visits each city exactly once and returns to the original city? Questions like this apply to challenges such as shipping logistics, flight scheduling, search optimization, DNA analysis and encryption, and are extremely difficult to answer quickly. The D-Wave computer has the greatest potential in this area, McGeoch says.

"This type of computer is not intended for surfing the internet, but it does solve this narrow but important type of problem really, really fast," McGeoch says. "There are degrees of what it can do. If you want it to solve the exact problem it's built to solve, at the problem sizes I tested, it's thousands of times faster than anything I'm aware of. If you want it to solve more general problems of that size, I would say it competes – it does as well as some of the best things I've looked at. At this point it's merely above average but shows apromising scaling trajectory."

McGeoch, who has spent her academic career in computer science, doesn't take a stance on whether the D-Wave is a true quantum computer or not, a notionsome physicists take issue with.

"Whether or not it's a quantum computer, it's an interesting approach to solving these problems that is worth studying," she says.

Whether the D-Wave computer will ever have mass market appeal is also difficult for McGeoch to assess. While the 439-qubit model she tested does have incredible computing power, there is that near-zero Kelvin chip operating temperature requirement that would make home or office use a chilly proposition. At present, she thinks the power of the D-Wave approach is too narrowly focused to be of much use to the average personal computer user.

"The founder of IBM famously predicted that only about five of his company's first computers would be sold because he just didn't see the need for that much computing power," McGeoch says. "Who needs to solve those big problems now? I'd say it's probably going to be big companies like Google and government agencies."

And, while conventional approaches to solving these problems will likely continue to improve incrementally, this fast quantum approach has the potential to expand to larger variety of problems than it does now, McGeoch says.

"Within a year or two I think these quantum computing methods will solve more and bigger problems significantly faster than the best conventional computing options out there," she says.

At the same time, she cautions that her first set of experiments represents a snapshot moment of the state of quantum computing versus conventional computing.

"This by no means settles the question of how fast the quantum computer is," she says. "That's going to take a lot more testing and a variety of experiments. It may not be a question that ever gets answered because there's always going to be progress in both quantum and conventional computing."

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## bertibus

## eachus

For example, cracking keys for most public key (actually non-symmetric key) systems will be a function of how many qbits your quantum computer can handle. At 439 qbits SSL2 is still safe, and I can't imagine any crooks managing to buy a several thousand qbit version anytime soon. But it is comming. (Shorr's algorithm for factoring numbers takes about 6 qbits per bit of key length. That doesn't mean that better algorithms are not possible...)

## Nawangsari

## NeutronicallyRepulsive

## Ryan1981

## antialias_physorg

It's qbit. Not bit.

While a qbit, like a classical bit, is classified by 2 states (e.g. polarization directions) a single qbit can be in a superposition of both - making it able to hold as much information as many (theoretically infinitely many) classical bits.

## Jo01

No, a qbit can hold the same information as a bit if you read it out. It has the information of two bits if its in superposition.

J.

## Higgsbengaliboson

## antialias_physorg

https://en.wikipe...._qubits

Careful. 'bit' is a unit of information logarithm base two of the number of possible states. qbit is not.

A 439 qbit memory can be in a superposition that would require 2^439 regular bits to represent (double that since they're complex states). Reading it out will get you only 439 bits. But here you already see that it's apples and oranges, because the storage/reading (as with regular memory registers) is not the main point of qbits

The point is that through this vast number of stored potential bits, choosing the right algorithm for reading out, you can get the answer in one go

Example: if all the combinations and permutations in a travelling salesman problem would need 2^439 bit to express you could solve the problem in one step using 439 qbits.

## Jo01

So, as I said: 1 qbit has the information of 2^1 bits and not as you stated in your previous comment: "...making it able to hold as much information as many (theoretically infinitely many) classical bits" which is clearly wrong.

So be careful yourself and acknowledge your wrong.

J.

## Foolish1

D-wave is cheating the search space of a single operation is not 2^439 or anything remotly resembling it. The state of the art today is around 8 entangled qbits if your really really lucky. There is no reason to believe we will ever be able to scale up the **exponents** without having to pay an impractical cost.

I have no doubt quantum computers are and will continue to be useful in the future but the quantum hype of exponential scaling (e.g. code breaking, classically impossible to solve NP problems..etc) smacks of magic to which we are not entitled.

## ValeriaT

## Pressure2

That pretty much sums it up ValeriaT.

I'll take it a step further, true quantum computers will never exist because superposition and quantum entanglement exist only in theory and have never been proven.

## gwrede

This sounds just like some scifi movie poster from the Fifties.

(YouTube "Earth vs. the Flying Saucers" trailer, in honor of sfx icon Ray Harryhausen, 92, who just died.)

## antialias_physorg

No. this is wrong.

You can READ OUT 1 bit. But you can store/manipulate a lot of bits worth of information in onwe qbit at a time.

Thinking of a qbit as a mere memory cell is wrong. It's apples and oranges. The superpositon of states let's you do stuff with it that would require a lot of calssical bits of storage (and algorithmic processing capability)

If you'd argue that a 1 bit computer has the same cpabilities as a 1qbit computer just because you can read one bit out then that would be as wrong as you can get.

## Jo01

You contradict your own statements. I never stated the last remark you made and I never compared a qbit to a memory cell.

So I wonder, do you agree with the following statement from a scientific paper:

"If there is a system of m-qubits, the system can contain information of 2^m states"

If so, then you must agree with "If there is a system of 1-qubits, the system can contain in- formation of 2^1 states"

## Jo01

So "1 qbit has the information of 2 bits".

QED.

J.

## antialias_physorg

No. A system of 1 qbit can READ OUT information that contains 1 bit. But the system can CONTAIN much more information.

qbit cells are not mere memory cells. You're comparing apples and oranges here.

You're comitting what we programmers call classical GIGO in your QED.

(GIGO: garbage in - garbage out. Which means: wrong assumptions lead to faulty conclusions).

## Jo01

Ha ha, I am a programmer (and amateur scientist) myself.

I might point out to my 'defense' that the starting axiom is from a scientific paper (and generally accepted for as far as I can see) and not from myself. So this means you reject a common scientific viewpoint. No laws (except logic in this case) against that.

The point is that 'information' relates to the information the (quantum) system handles and not the state of (quantum) system itself. In other words: we aren't simulating the quantum system itself and the (cont)

## Jo01

J.

## megmaltese

## baudrunner

## megmaltese

Traditional CPU needed 6 hours, QBIT CPU solved in 5 minutes?

Why?

## ValeriaT

## antialias_physorg

No. Read the wikipedia link. The maximum information contained (and processed) is much more. You're still thinking classical bit cells.

qbit cells are not memory cells in the classical sense.