01 Filtering the Future QUANTUM ISSUE 03 JUN 2017 COMPUTING QUANTUM COMPUTERS AND THE POTENTIAL APPLICATIONS OF THIS REVOLUTIONARY TECHNOLOGY images: Docubytes, © by James Ball © by Docubytes, images: INTRODUCTION INTRODUCTION FILTERING THE FUTURE IS BASED ON THE MOST EXCITING AND SIGNIFICANT MESSAGES OF THE FILTER FROM THE LAST MONTHS. THIS FILTERING THE FUTURE IS ABOUT QUANTUM COMPUTERS AND THE POTENTIAL APPLICATIONS OF THIS REVOLUTIONARY TECHNOLOGY. FILTERING THE FUTURE / QUANTUM COMPUTING 03 WHAT IS QUANTUM COMPUTING? Everything in the natural world can be described by quantum mechanics, and doing so has led to the development of everyday technologies from MRI scans, nanotechnology and the transistor. There are two quantum revolutions. The first one was in (quantum) physics: understanding how things work at the sub-atomic level, and that yielded some strange conclusions: particles can be in two states at the same time; two or more particles that are separated at great distance can still ‘sense’ each other; the exact position of a particle is never certain until it is measured or observed but this observation or measurement changes the situation of the particle irrevocably. In the 1920s, quantum physicists did the math that underpins these conclusions, but they were made manifest in laboratory experiments only later on in the 20th century. The practical work on quantum computing – the second quantum revolution – started in the 1980s, with the work of Paul Benioff and Yuri Manin, Richard Feynman, and David Deutsch, when scientists learned how to apply the physics and mathematics to model computers that could perform ‘quantum computations’. The main idea is that a quantum computer programs atoms to represent all possible input combinations simultaneously and run an algorithm that tests all possible combinations at once, instead of serially cycling every possibility by varying input to arrive at a solution. This method will help to solve the most complicated computations that even modern-day supercomputers take decades to do. Why? Because quantum computation is conceptually different from ‘normal computation’, or the way ‘traditional’ computers perform their operations. Three concepts - that defy our intuition - are at the center. The first is superposition. Traditional computing depends on bits that can only take on two, binary values: 0 or 1. Qubits, their quantum analogues, can be arranged in ‘states’: something like a mixture of 0, 1 or both 0 and 1 (tertiary value). To carry out a quantum computation with qubits is to act on the 0, 1 and both at the same time. WHAT IS QUANTUM COMPUTING? The concept of entanglement unleashes the power of these indeterminate state of qubits. Binary bits in a traditional computer are isolated from another, but inside a quantum computer all qubits are interrelated or correlated, or ‘entangled’ with another. And a quantum computer can run its computations on all ‘entangled superpositions’ simultaneously. That means that to operate on one qubit is to operate on all entangled qubits, making the computational power of a quantum computer an exponential function of its qubits (computational power = 2^qubits), impossible to describe by decomposing it into its constituent parts. For example, to describe all the states of a (binary) 50-bit traditional computer requires 50 bits of digital memory; a description of a (entangled) 50-qubit quantum computer would require 2.5 quadrillion (see for example IBM’s recent handbook on numerical benchmarks for quantum computing to define the computational power of quantum computing, or ‘volume’ of quantum computers). That brings us to the last quantum concept: its probability amplitude. Equations in traditional computing can predict the probability of a given event, for example how likely it is that the S&P will decline by 10% or the chance the Ajax wins the Europe League. But probabilities in quantum computing – which can also be negative – can interfere with each other and depend on the other elements of the probability equation that is used. So when a quantum computer searches a data set for example, it can take shortcuts to the right answer. It does so by reducing the probability of wrong answers and increasing the probability of the right answers from its own operations. These three properties make quantum computing so different of traditional computing, because quantum computing reverses the order and concept of a computation. Traditional computing systems deliver the output (the answer) given the input (the question). Consider, for example, that we want to know all possible computations of the number ‘1000’, using only prime numbers. Because traditional computing is binary, with isolated events and fixed probabilities, it will start factoring FILTERING THE FUTURE / QUANTUM COMPUTING 05 all possible operations with prime numbers that yield the number ‘1000’. The problem for the system is the ‘problem’ itself: what we want to know, our question. But quantum computing works otherwise, because its system uses programmed atoms that already contain every possible answer, and the problem is how to ask it. In other words, the quantum system already knows or contains how many prime number operations yield the number ‘1000’, and we only need to put the right question. So the quantum system no longer considers the operation as an ‘or…or problem’ (binary) but as ‘and…and’ (entangled superpositions) as it ‘recognizes’ all the right answers immediately that are inherent to the system. The problem is not the computation of all possible combinations or all the steps in the computational linkage, but only to filter all right answers. And that saves a lot of time. So quantum computing is both conceptually and technologically a real ‘paradigm shift’ from traditional computing. Companies are therefore rushing to make the first working quantum computer, to reach ‘quantum supremacy’: performing certain calculations traditional computers cannot do, like some physical processes cannot be emulated by non-quantum models. Some computations are so complex or large that traditional (super)computers cannot perform these in a finite time slot or would otherwise require an almost infinite amount of energy. Quantum computing can tackle these problems. DEVELOPING QUANTUM COMPUTERS FILTERING THE FUTURE / QUANTUM COMPUTING 07 DEVELOPING QUANTUM COMPUTERS Until now, researchers only succeeded to build five-qubit computers and more fragile 10- to 20-qubit test systems. But the head of Google’s quantum computing effort, Harmut Neven, claims his team is on target to build a 49-qubit system by as soon as a year from now. And this target of around 50 qubits isn’t an arbitrary one: it’s the threshold of quantum supremacy. In other words, today’s top supercomputer systems can more or less still do all the same computations these 5- to 20-qubit quantum computers can do, but at around 50 qubits this becomes impossible. But quantum computing also has its own obstacles. It is for example very expensive. That’s because quantum computers can only operate in very controlled conditions, as qubits are extremely susceptible to noise, vibrations, temperature, or fluctuating electric fields. Entangled superpositions can only be reached in ‘pure’ states, that are often just above the absolute zero of -273,15°. Creating and sustaining these conditions therefore requires a lot of energy, money and time. Not to mention the costly process of engineering and hosting quantum computers, using and creating new and rare quantum materials, and working on the edge of scientific knowledge where no one has been before and no idea seems crazy or counter-intuitive enough. That does not withhold scientists and companies to invest and experiment with quantum computing. According to MIT, all the academic and corporate quantum researchers agree that somewhere between 30 and 100 qubits - particularly qubits stable enough to perform a wide range of computations for longer durations - is where quantum computers start to have commercial value, and as soon as two to five years from now, such systems are likely to be for sale. In the long run, they expect 100,000-qubit systems or even a million-physical-qubit system could be engineered and become functional. That will put quantum computing at an unsurmountable distance to traditional computing systems and perform computations that are for now unconceivable One place where pioneering work is done is in the Netherlands, Delft, where QuTech DEVELOPING QUANTUM COMPUTERS is experimenting to design a quantum computer and a new kind of qubit. A team of scientists, led by Leo Kouwenhoven, believes the qubits they are creating, called Majorana’s, will be the building blocks for their stable and functioning quantum computer and quantum internet, because of their unique physical properties. Further breakthroughs in quantum computing’s development process came recently, when an international team of scientists published a plan to build a huge quantum computer. The device, proposed in the journal Science Advances, will be as large as a football field and cost upwards of $125 million. The proposed design uses magnetic fields to trap ions, which would be used as qubits and controlled via microwaves. Intriguingly, the team claims that it could be built now, arguing that components required for the system have been demonstrated in labs. In theory, it would be far more powerful than all currently available systems. But researchers would have to face up to many engineering problems, like how to string the elements together and ensure it all stays cool. “Such high-level issues are rarely considered by people in the field of quantum computing, either because they think it’s goofy to think that big, or because in their own physical system, it is nearly impossible to fathom such a high-level view” said Christopher Monroe, a physicist from University of Maryland in College Park, to Nature. And recently, scientists from the Ion Quantum Technology Group at Sussex University claimed to produce the first ever blueprint for a large- scale quantum computer.