D-Wave's Quantum Computer Successfully Models a Quantum System (arstechnica.com)

An anonymous reader shares an excerpt from Ars Technica: D-Wave's hardware has always occupied a unique space on the computing landscape. It's a general-purpose computer that relies on quantum mechanical effects to perform calculations. And, while other quantum-computer makers have struggled to put more than a few dozen qubits together, D-Wave's systems have already scaled to more than 2,000 addressable bits. But the D-Wave systems don't perform calculations in the same way and, despite all those bits, haven't clearly demonstrated performance that can outpace even traditional computing hardware. But D-Wave has come out with a research paper in Science that suggests that the system can do interesting things even in its current state. The company's researchers have set it loose modeling a quantum system that closely resembles the bits used in the hardware itself, allowing them to examine quantum phase transitions. While this still isn't cutting-edge performance, it does allow researchers full control over the physical parameters of a relevant quantum system as it undergoes phase changes.

Comments

This is not the quantum computer you think...

[Anonymous Coward]

I'm a scientist in the quantum information technology area. It always annoys me to see the marketing machine of D-Wave trumpeting their number of qubits as the ultimate achievement in quantum computing. I could point you to Scott Aaronson's great blog, but the bottom line is: THIS IS NOT A GENERAL-PURPOSE COMPUTER, EVEN LESS OF A GENERAL-PURPOSE QUANTUM COMPUTER.

You see, the power of a QC is not just in the number of qubits. But even assuming this were the case, qubits come in different "quality". If you want to run Shor's algorithm, or in general all those computational tasks that highlight the alleged superiority of a QC, you need qubits of very high "quality" - in terms of entanglement, noise, programmability, etc. The current approach of companies such as Google, IBM, Rigetti, is to try to get a bunch of qubits as "pure" as possible. You can already run Shor's algorithm on IBM's Q cloud quantum computers for example, however these machines are limited to very few qubits - I think the current record is Google's Bristlecone at 72 qubits, and it's not publicly peer-reviewed yet, the only one which has been academically scrutinized is the IBM's 20 qubits one I think. The core reason is the following: building a QC with, say, 20 qubits does not mean sticking together two QC with 10 qubits each. The engineering difficulty is not "double" as much as building a QC with 10 qubits: it grows exponentially.

D-Wave's approach is totally different. They just stick together a bunch of very "dirty" qubits (completely useless for quantum computing in general), but optimize their machines to solve faster certain problems. The specific problems they solve is basically "simulate a D-Wave machine" (!!!) Kidding apart, these machines only solve certain VERY SPECIFIC physical simulation problems. However, these problems are so specific that there is currently no proof whatsoever that D-Wave's machines offer a speedup over classical algorithms at all!

So, bottom line: no, D-Wave's machines are not going to crack your RSA key anytime soon.

Adiabatic quantum computing

[gotan]

The D-Wave is an "adiabatic quantum computer".
See: https://en.wikipedia.org/wiki/...

This is quite different from quantum Turing machines /universal quantum computers which is usually referred to as quantum computers.

Basically the D-Wave allows to search for a ground state in a system where the quantum states interact in a well controlled way.

The quantum states might represent logical bits, the interactions logical clauses (e.g. A & B = 1) and one might seek a state in which as many clauses as possible are satisfied. Such problems are known as SAT (satisfiability) problems.

Another application could be, that the quantum states represent e.g. (valence) electrons in a crystal lattice (preferably a metal), which interact with their neighbors. The ground state of such a system might give insights to magnetic properties of (abstract models of) materials (when the interaction makes electron spins flip in a coherent manner that might cause ferromagnetism). Determining such ground states with classical computing can quickly lead to time- and memory demanding problems even for few quantum states.