PORTLAND, Ore.—Recently I had to explain to a reader why critics say that D-Wave's so-called quantum computer was not a "real" quantum computer, the answer for which he accepted on my authority. However, the question kept nagging me in the back on my mind "why" D-Wave markets what it calls a quantum computer if it is not for real. To get to the bottom of it, I asked Jeremy Hilton, vice president of processor development of D-Wave Systems, Inc. (Burnaby, British Columbia, Canada) about why critics keep saying its quantum computer is not for real. He also revealed details about D-Wave's next generation quantum computer.
"The Holy Grail of quantum computing to build a 'universal' quantum computer—one that can solve any computational problem—but at a vastly higher speed that today's computers," Hilton told EE Times. "That's the reason some people say we don't have a 'real' quantum computer—because D-Wave's is not a 'universal' computer."
D-Wave's quantum computer, rather, only solves optimization problems, that is ones that can be expressed in a linear equation with lots of variables each with its own weight (the number that is multiplied times each variable). Normally, such linear equations are very difficult to solve for a conventional 'universal' computer, taking lots of iterations to find the optimal set of values for the variables. However, with D-Wave's application-specific quantum computer, such problems can be solved in a single cycle.
"We believe that starting with an application-specific quantum processor is the right way to go—as a stepping stone to the Holy Grail—a universal quantum computer," Hilton told us. "And that's what D-Wave does—we just to optimization problems using qubits."
D-Wave's 512 superconducting niobium qubits on a silicon substrate.
D-Wave's current quantum processor has 512 qubits, allowing it to solve optimization problems with less than or equal to 512 variables in single machine cycle. To solve qubit-based optimization problems, D-Wave uses a different model for computation than a universal computer, called the adiabatic (occurring without loss or gain of heat) instead of the approach take by everyone working toward a universal quantum computer—the normal gates-based model when qubits are processed in the quantum computer in a manner similar to conventional computers.
"The goal of the adiabatic method is to keep the qubits in their lowest energy state, which is where they are at the beginning and end of a optimization problem," Hilton told us. "When the weights of the variables are input the qubits go into an excited state, but quickly relax into their lowest energy state, thereby revealing the optimal values of the variables."
D-Wave gets about 100 quantum computer chips per wafer (two shown here) which is mounts on a super-cooled mounting (middle below).
Those working toward a universal quantum computer today are obsessed with error correction methods—using up to thousands of qubits just to ensure that the superposition of values in a quantum state (part 0 and part 1) is maintained accurately throughout all of its calculations. With the adiabatic method, Hilton claimed, you don't need error correction because the qubits naturally relax into their lowest energy state.
"Our qubits go from excited level to a relaxed level, they don't need error correction at this point," Hilton told us. "But with gate-model of a universal quantum computer you need error correction to get anything to work at all."
Companies are investing
"What struck me when I talked to D-Wave is that they are rather modest," Mike Battista, senior manager and analyst of Infrastructure at Info-Tech Research Group. (London, Ontario, Canada) told EE Times. "They are excited about their technology, but don’t over-promise on its potential."
Battista also cited how D-Wave is pioneering more than just quantum computing, but also accumulating experience with new paradigms—like superconductivity—that could keep Moore's Law going.
Jeremy Hilton, vice president of processor development of D-Wave, holding the "Vesuvius" 512-qubit module that will be supercooled down to .2 milliKelvin using a 10kWatt refrigerator.
"Their superconducting semiconductors have advantages even outside of being able to perform quantum computing, such as releasing no heat at all," Battista told us. There is also the potential for the technology to improve exponentially, perhaps being able to carry the next paradigm that continues Moore’s Law when traditional transistors reach their physical limits."
When asked why critics claims its not a "real" quantum computer and they should not be calling it such, Battista had a reasoned answer as to why its going the right direction.
"I know testing of the D-Wave hardware has been mixed, but I understand why large companies are investing in it anyway," Battista told us. "If there is even a small chance that this is the next foundational technology that underlies computing for the next few decades, the investments will be worth it. Companies that get a head start in developing algorithms and finding problems that are amenable to quantum computing will be at a huge advantage if/when viable hardware emerges."
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