### World’s largest quantum computation uses 84 qubits

##### January 12, 2012

D-Wave Systems has carried out a calculation involving 84 qubits on its D-Wave One quantum computing system, *Technology Review Physics arXiv blog* reports.

Their complex task was to calculate various “two-color Ramsey numbers,” connected with the emergence of order in disordered systems.

Ref.: Zhengbing Bian et al., Experimental Determination Of Ramsey Numbers With Quantum Annealing, arxiv.org/abs/1201.1842

## comments 8

January 13, 2012by Giulio Prisco

I agree with dougw659, QC may become a game changer and have a very big impact in the future, but not tomorrow or next week, and probably not next year or next decade either. At the same time, practical application will come, and the very possibility of QC has interesting theoretical implications now and may shed new light on fundamental physics.

January 12, 2012by policetac

The D-wave One superconducting 128-qubit processor chip is housed inside a cryogenics system within a 10 square meter shielded room. The technology is so efficient that processors with 1000x the computing power can be created with very little increase in power consumption.

January 12, 2012by dougw659

hmmm maybe not, unless by ‘your life’ you really mean human life in the future. Considering the current problem of keeping entangled particles from decohering does not look all that easy to solve, it may be many, many years before Quantum Computing is any more than an interesting research project….

January 12, 2012by policetac

I believe that D-wave is slightly past the “interesting research project” stage.

In May of 2011, D-Wave Systems made history by announcing the sale of the world’s first commercial quantum computer. The buyer was Lockheed Martin Corporation, who will use the machine to help solve some of their “most challenging computation problems.” Lockheed purchased the system, known as D-Wave One, as well as maintenance and associated professional services

D-Wave’s initial system has just 128 qubits–and they need to be treated very carefully to work as they are supposed to. The system needs to be kept near absolute zero–minus 459 degrees Fahrenheit–and carefully shielded to avoid interference from magnetic radiation. Daniel Lidar, scientific technical director of the new USC center, calls it one of the coldest and most magnetically shielded places on earth.

January 12, 2012by codesimian

That is not an 84 qubit computer because its bandwidth is bottlenecked by the single entanglement between 2 “qubits” connecting large sections of many “qubits”. Its like calling your computer a billions of bits computer instead of a 32 bit computer, because its RAM has billions of bits, and its CPU only calculates 32 bits at a time. That is approximately an 8 qubit computer.

January 12, 2012by policetac

A quantum computer with a given number of qubits is fundamentally different from a classical computer composed of the same number of classical bits. For example, to represent the state of an n-qubit system on a classical computer would require the storage of 2n complex coefficients. Although this fact may seem to indicate that qubits can hold exponentially more information than their classical counterparts, care must be taken not to overlook the fact that the qubits are only in a probabilistic superposition of all of their states. This means that when the final state of the qubits is measured, they will only be found in one of the possible configurations they were in before measurement. Moreover, it is incorrect to think of the qubits as only being in one particular state before measurement since the fact that they were in a superposition of states before the measurement was made directly affects the possible outcomes of the computation.

Qubits are made up of controlled particles and the means of control (e.g. devices that trap particles and switch them from one state to another).[8]

For example: Consider first a classical computer that operates on a three-bitregister. The state of the computer at any time is a probability distribution over the23 = 8 different three-bit strings 000, 001, 010, 011, 100, 101, 110, 111. If it is a deterministic computer, then it is in exactly one of these states with probability 1. However, if it is a probabilistic computer, then there is a possibility of it being in anyone of a number of different states. We can describe this probabilistic state by eight nonnegative numbers A,B,C,D,E,F,G,H(where A = probability computer is in state000, B = probability computer is in state001, etc.). There is a restriction that these probabilities sum to 1.

The state of a three-qubit quantum computer is similarly described by an eight-dimensional vector (a,b,c,d,e,f,g,h), called a ket. However, instead of adding to one, the sum of the squares of the coefficient magnitudes, | a | 2 + | b | 2 + … + | h | 2, must equal one. Moreover, the coefficients are complex numbers. Since the probability amplitudes of the states are represented with complex numbers, the phase between any two states is a meaningful parameter, which is a key difference between quantum computing and probabilistic classical computing.[9]

If you measure the three qubits, you will observe a three-bit string. The probability of measuring a given string is the squared magnitude of that string’s coefficient (i.e., the probability of measuring 000 = | a | 2, the probability of measuring 001 = | b | 2, etc..). Thus, measuring a quantum state described by complex coefficients (a,b,…,h) gives the classical probability distribution ( | a | 2, | b | 2,…, | h | 2) and we say that the quantum state “collapses” to a classical state as a result of making the measurement.

Note that an eight-dimensional vector can be specified in many different ways depending on what basis is chosen for the space. The basis of bit strings (e.g., 000, 001, …, 111) is known as the computational basis. Other possible bases are unit-length, orthogonal vectors and the eigenvectors of the Pauli-x operator. Ket notation is often used to make the choice of basis explicit. For example, the state (a,b,c,d,e,f,g,h) in the computational basis can be written as:

where, e.g.,

The computational basis for a single qubit (two dimensions) is and .

Using the eigenvectors of the Pauli-x operator, a single qubit is and .

January 12, 2012by dziukap

I think a lot of people, even some of the tech savvy ones who regular this site, don’t really get what they are seeing here. This is like watching Edison tinker with is first light bulbs. Quantum computing is the way through the rabbit hole for our current processing limitations. It will change your life as much as any other past technological revolution, perhaps even more.

January 12, 2012by policetac

Now you I can wholeheartedly agree with! :)