The Era of Quantum Computing Microprocessors Dawns
 
Many of the toughest problems in medicine, chemistry, nano-technology and cyber-security, simply can’t be solved using conventional digital computing technology.  That’s where quantum computing comes in.  And that’s why, when we wrote Ride the Wave, we identified quantum computing as one of the 12 crucial technologies needed to fully realize the potential of the Digital Techno-Economic Revolution.

Unfortunately, creating a general-purpose quantum computer has proven to be overwhelmingly difficult.  And the resulting hardware prototypes have proven about as reliable and maintainable as the original vacuum tube technology used in the Eniac system.  Today’s only commercial quantum computer is from D-Wave Technologies; it uses a highly specialized approach called “quantum annealing” to solve a narrow range of optimization problems for cutting-edge companies, like Google and Lockheed-Martin, who are willing to pay over $10 million per machine.

In the meantime, research teams all over the world have been exploring different ways to design a working computer that can integrate quantum interactions.  But, a complete engineering design to realize this on a single chip has been elusive.

However, that’s about to change. It seems we are on the verge of a technological leap that could be as deep and transformative as the original microprocessor release in 1973.

Engineers at the University of New South Wales, or UNSW, believe they have solved the problem by re-imagining the silicon microprocessors we know, to create a complete design for a quantum computer chip that can be manufactured using mostly standard industry processes and components.

The new chip design, published recently in the journal Nature Communications, involves a novel architecture that allows quantum calculations to be performed using existing CMOS technology, the basis for all modern chips. As remarkable as they are, todays computer chips cannot harness the quantum effects needed to solve the important problems that quantum computers will.  The power of the new design is that, for the first time, it charts a conceivable engineering pathway toward creating a machine with millions of quantum bits, or qubits.

To solve problems that address major global challenges -- like secure encryption or complex diseases -- its generally accepted that we will need millions of qubits working in tandem. To do that, we will need to pack qubits together and integrate them, like we do with modern microprocessor chips. Thats what this new design aims to achieve.

This design uses conventional silicon transistor switches to turn on operations between qubits in a vast two-dimensional array, using what engineers call “a grid-based word and bit select protocol,” which is similar to that used to select bits in a conventional computer memory chip.  By selecting electrodes above a qubit, they can control a qubits spin, which stores the quantum binary code of a 0 or 1.  And by selecting electrodes between the qubits, two-qubit logic interactions, or calculations, can be performed between qubits.

A quantum computer exponentially expands the vocabulary of binary code used in modern computers by using two “spooky principles” of quantum physics -- namely, entanglement and superposition.  Qubits can store a 0, a 1, or an arbitrary combination of 0 and 1 at the same time. And just as a quantum computer can store multiple values at once, so it can process them simultaneously, doing multiple operations at once.

This allows a universal quantum computer to be millions of times faster than any conventional computer when solving a wide range of important problems.  But to solve these complex problems, a useful universal quantum computer will need a large number of qubits, possibly millions.

That’s because every type of qubit we know is fragile and even tiny errors can be quickly amplified into wrong answers.  So, we need to use error-correcting codes which employ multiple qubits to store a single piece of data.  The UNSW chip blueprint incorporates a new type of error-correcting code designed specifically for spin qubits, and involves a sophisticated protocol of operations across the millions of qubits.  This design represents the first attempt to integrate into a single chip all of the conventional silicon circuitry needed to control and read the millions of qubits needed for real-world quantum computing.

The researchers expect that modifications will still be required to this design as they move towards manufacture.  But all of the key components that are needed for quantum computing are now here in one chip. And thats what will be needed to make quantum computers the workhorses for calculations that are well beyond todays computers.

The effort to design and build such a universal quantum computer has been called the space race of the 21st century.  That’s because, for some challenging problems, they could find solutions in days, or maybe even hours, which would take millions of years using todays best supercomputers.

Today, there are at least five major quantum computing approaches being explored worldwide:

- silicon spin qubits,
- ion traps,
- superconducting loops,
- diamond vacancies, and
- topological qubits.

UNSWs design is based on silicon spin qubits.

The main problem with all of these approaches is that there has been no clear pathway to scaling the number of quantum bits up to the millions needed without the computer becoming a huge system requiring bulky supporting equipment and costly infrastructure.

The UNSW design, for the first time, incorporates everything needed to integrate the millions of qubits needed to realize the true promise of quantum computing on a single chip.

Thats why UNSWs new design is so exciting.  By relying on its silicon spin qubit approach -- which mimics the solid-state devices in silicon that are the heart of the $380 billion a year global semiconductor industry -- it shows how to dovetail spin qubit error correcting code into existing chip designs, enabling true universal quantum computation.
 
Unlike almost every other major group, the UNSW quantum computing effort is obsessively focused on creating solid-state devices in silicon, from which all of the worlds existing computer chips are made. And theyre not just creating ornate designs to show off how many qubits can be packed together; they are aiming to build qubits that could be easily fabricated -- and scaled up.

This design represents a big leap forward in silicon spin qubits.  It was only two years ago, in a paper in Nature, that its developers revealed the creation of a two-qubit logic gate -- the central building block of a quantum computer. It showed, for the first time, how quantum logic calculations could be done in a real silicon device.

Those were the first “baby steps,” demonstrating how to turn this radical quantum computing concept into a practical device using components that underpin all modern computing.  And now the UNSW team has a blueprint for scaling that up dramatically.

They’ve been testing elements of this design in the lab, with very positive results. They just need to keep building on that.

Given this trend, we offer the following forecasts for your consideration.

First, until reliable general-purpose hardware is available quantum computing will remain a sleeping giant.

Quantum computing is still at the stage where digital computing was in the late1940s: laboratory prototypes and conceptual designs with only theoretical applications. That was all changed by the invention of solid-state transistor logic gates. But, once a reliable quantum processor exists, software and new applications will explode.

Second, over the next five years, companies and nations will make lots of small bets on quantum computing and a few will pay-off big.

For example, in August 2017, the UNSW researchers launched Silicon Quantum Computing Pty Ltd. It’s Australias first quantum computing company, intended to advance the development and commercialization of the teams unique technologies. And it just struck an $83 million deal to develop, by 2022, a 10-qubit prototype silicon quantum integrated circuit.  That will represent the next big step toward building the worlds first quantum computer in silicon.  And,

Third, it will be at least a decade before we know for certain which of the six computing qubit technologies will dominate quantum computing in same way CMOS dominates conventional computing.

The outcome will depend on which technological approach ultimately creates the most efficient universal quantum computer that can be scaled up, at a reasonable cost, to solve problems beyond the capabilities of conventional supercomputers.  And history is replete with examples where its not the best technology that gains a foothold, or the cheapest, or even the one that scales up fastest.  It may possibly take several iterations; remember, it took four generations of computers to get from bulky vacuum tube circuitry and magnetic drum memory to the multi-core CPUs with silicon semiconductor logic gates, common today.

References
1. Nature Communications, 2017. Veldhorst, H. G. J. Eenink, C. H. Yang, A. S. Dzurak. Silicon CMOS architecture for a spin-based quantum computer.

https://www.nature.com/articles/s41467-017-01905-6 

2. Nature Communications, 2017. Guilherme Tosi, Fahd A. Mohiyaddin, Vivien Schmitt, Stefanie Tenberg, Rajib Rahman, Gerhard Klimeck, Andrea Morello. Silicon quantum processor with robust long-distance qubit couplings.

https://www.nature.com/articles/s41467-017-00378-x

3. Cosmos, SEPTEMBER 13, 2017. Wison da Silva. The quest for a silicon quantum computer,

https://cosmosmagazine.com/technology/the-quest-for-a-silicon-quantum-computer

4. Science, December 7, 2017.  D. M. Zajac, A. J. Sigillito, M. Russ, F. Borjans, J. M. Taylor, G. Burkard, J. R. Petta. Quantum CNOT Gate for Spins in Silicon.

https://www.researchgate.net/publication/319101407_Quantum_CNOT_Gate_for_Spins_in_Silicon