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31

Google, IBM and Rigetti use transmon qubits; these are basically fancy LC circuits where a Josephson junction and capacitor connect two superconducting islands. Because of this, they are also often referred to as superconducting qubits. The qubit states are the various charge levels that can exist on the circuit; since the lowest two levels are separated in ...


28

There is still a search for problems where the D-Wave shows improvement over classical algorithms. One might recall media splashes where the D-Wave solved some instances $10^8$ times faster than a classical algorithms but forgot to mention that the problem can be solved in polynomial time using minimum weight perfect matching. Denchev showing $10^8$ ...


26

The 'Hello World' equivalent in the D-Wave world is the 2D checkerboard example. In this example, you are given the following square graph with 4 nodes:                                   &...


18

A Quantum Annealer, such as a D-Wave machine is a physical representation of the Ising model and as such has a 'problem' Hamiltonian of the form $$H_P = \sum_{J=1}^nh_j\sigma_j^z + \sum_{i, j}J_{ij}\sigma_i^z\sigma_j^z.$$ Essentially, the problem to be solved is mapped to the above Hamiltonian. The system starts with the Hamiltonian $H_I = \sum_{J=1}^nh'_j\...


16

Annealing's more of an analog tactic. The gist is that you have some weird function that you want to optimize. So, you bounce around it. At first, the "temperature" is very high, such that the selected point can bounce around a lot. Then as the algorithm "cools", the temperature goes down, and the bouncing becomes less aggressive. Ultimately, it settles ...


12

Short explanation: D-Wave implements quantum annealing, while Google has digitized adiabatic quantum computation. Lengthy Explanation: D-Wave advertises their line of quantum computers as having thousands of qubits, though these systems are designed specifically for quadratic unconstrained binary optimization. More information about D-Wave's manufacturing ...


11

There are two points I'd make here. D-Wave's computer and Google's computer are fundamentally different. D-Wave's computer is a quantum annealer. Imagine a landscape with some grassy hills. If you put a ball at the top of the hill, it will roll to a local minima, or even the minimum - in this case, a valley. Similarly, a quantum annealer has the qubits as ...


10

As Troyer and Lidar saw no speed increase with the D-Wave 1 compared to classical computers, the D-Wave 2 benchmark figure reported in 2013 of 3600 times as fast as CPLEX (the best algorithm on a conventional machine) suggests the D-Wave 2 is 3600 times as fast as the D-Wave 1. However: the results are in a pretty restricted set of parameters, so this may ...


9

The title and question body seem to ask two different questions. In the title you ask "How do you write a simple program for a D-Wave device?", while in the question body you ask how to find the ground states of a simple 2D Ising model using the underlying hardware of the D-Wave device, and what the corresponding code would be (which is a more specific ...


8

In the classical case, there is a pretty big difference between digital computers and analogue ones. The methodology and hardware is very much distinct (in all cases I know of, at least). The divide is still there in the quantum case, but it doesn't run quite as deep. The hardware can be similar, but requirements on how it behaves and how to manipulate it ...


8

Is there proof that the D-wave (one) is a quantum computer and is effective? D-Wave Video - Offers an explanation of: "How do we know ...": https://youtu.be/kq9VqR0ZGNc One analogy you might make with the D-Wave One, an adiabatic ('analog') computer, is to the "south-pointing chariot" or the "Antikythera mechanism". A lengthy explanation is offered in ...


7

Pressure implies the presence of stray atoms flying around messing things up. The use of a vacuum is required to prevent this, as one of the ways of keeping the device well isolated from unwanted effects. I think that they are just intending the "10 billion times lower than atmospheric pressure" statement to demonstrate how good their vacuum is.


7

As far as I know the closest answer to your question for applications is given in the recent (still unpublished) work presented at the March meeting by Bibek Pokharel, where he compares graph 3-coloring instances on D-Wave Two, D-Wave 2X and D-Wave 2000Q, all other things staying reasonably equal. The short answer is that all the performance increase is ...


7

The DWave machine relies heavily on single-flux-quantum digital control for setting up qubit and coupler operating points, and for carrying out the annealing protocol. Any stray magnetic flux, if present while the chip is cooled through its superconducting transition, will be trapped inside the circuit and can cause it to fail. You can calculate how much ...


7

So I do not know much about yacht design but having played a little bit with a D-Wave machine I would suggest to see if you can model your problem as a Quadratic unconstrained binary optimization. See on Wikipedia. That is your variables must be binary and a D-Wave machine will try to find a minimum to your QUBO. It will return many answers in a sense that ...


7

In the mentioned context, what is meant is that, between a pair of qubits that are coupled, an XX coupling means something of the form $$ X\otimes X\equiv\left(\begin{array}{cccc} 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \\ 0 & 1 & 0 & 0 \\ 1 & 0 & 0 & 0 \end{array}\right), $$ tensored with identity between all other ...


6

The inputs to the D-Wave are a list of interactions and more recently the annealing time of the qubits. As you mentioned the Ising problem is one of the easiest with $J_{ij} = 1$ in the problem Hamiltonian however it's not very interesting. I recommend the appendices in this paper for a concise description of how the D-Wave hardware operates. (Full ...


6

Yes, they use $\require{\mhchem}\ce{^3He}$ and $\ce{^4He}$. No, they do not use compounds of these but instead a solution of these two (at the operating temperature) liquid nobel gases. The details can be found in the wikipedia article on dilution refrigerators.


5

Pegasus is the first fundamental change in D-Wave's architecture since the D-Wave One. The D-Wave Two, 2X, and 2000Q all used the "Chimera" architecture, which consisted of unit cells of $K_{4,4}$ graphs. The four generations of D-Wave machines just added more qubits by adding more and more unit cells that were the same. In Pegasus, the actual structure of ...


5

The device works at cryogenic temperatures, which is so cold that all the gasses would freeze on the experiment device. Moreover, before they do so, they would conduct heat from the walls of the chamber to the experiment device and make it hard to cool the device down. Thus, you need vacuum for being able to cool things down to a very low temperature, and ...


5

XX couplers are necessary to make an quantum annealing universal. https://arxiv.org/abs/0704.1287 As for fabricating them, I’m not too familiar with the hardware issues. Perhaps someone else can comment on that.


5

The earliest non-internal reference I can find is in NIPS 2009 from a Google/D-Wave effort1. You'll notice that the two Choi papers, in addition to not using the term "Chimera", do not describe a Chimera graph (and note that the name comes from D-Wave, not from graph theory). For a good early reference on Chimera, I recommend Bunyk et al., 20141 , which ...


5

Moore's law deals with the number of transistors in an integrated circuit, which is used as a proxy for computational power. In a quantum computing device the analogy would be the number of qubits. However, this by itself would be a poor benchmark, namely because it is easy to build lots of qubits. Building many qubits with properties such as long ...


4

Until recently, D-Wave's quantum annealing devices always started from a uniform superposition over all $N$ qubits:                                         &...


4

You are right that $K_{3,3}$ is non-planar, but as you said yourself, a larger $k$ is much better. If they could do $K_{1000,1000}$ that would be nice, because each qubit could be coupled to 1002 qubits (1000 within the $K_{1000,1000}$ and two to the neighboring cells). Instead D-Wave is limited to problems which can be embedded such that each qubit couples ...


4

On parameter setting, check our work: https://journals.aps.org/prx/abstract/10.1103/PhysRevX.5.031040 (Basically you want to make sure that the chains representing the logical qubit have a phase transition synchronized with the minimum gap). But in general this is a hard problem, and precision issues connected to the embedding characteristics are probably ...


4

There are multiple factors that affect an embedding's performance, including what Davide mentions. Depending on your background, the following interpretation of Davide's answer might be easier for you to understand: Early in the anneal, the Ising (classical/user-input/final) Hamiltonian has no effect, which means that two spins in a chain are not compelled ...


4

When referring to the commercial quantum computers of both parties, it is that both are based on a different quantum principles. The D-Wave machine works via quantum annealing and is suited for optimization problems. The machine by IBM is a gate-based quantum computer, similar to how digital computers work at the elementary level. As the two quantum ...


4

Currently, it is not preciselly known whether quantum annealers bring any significant speed up. Lets take some task having exponential complexity on classical computer. If you run it on quantum annealer it will probably run faster. However the reason is not reduced complexity (it is still exponential) but smaller constants in function decribing the task ...


3

Quantum annealing as defined by Chakrabarti 1981 and later implemented by Kadowaki and Nishimori 1998 uses a varying transverse magnetic field to facilitate tunneling through the energy landscape of an optimization problem. The system is prepared in the ground state of a Hamiltonian and then the transverse field is applied and slowly reduced (adiabatically) ...


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