The technological challenge is immense. But the unique properties of quantum systems offer tantalizing power.
Excerpted from The Future Postponed, Massachusetts Institute of Technology, 2015
Karl K. Berggren: Director of the Nanostructures Laboratory in the Research Laboratory of Electronics, and Professor of Electrical Engineering in the Department of Electrical Engineering and Computer Science
What if we could harness the bizarre and counter-intuitive physics of the quantum world to create a real- world technology revolution? What if it offered computing power that could dwarf today’s supercomputers; unhackable long-distance communications systems, ways to measure time, electrical and magnetic properties, and other phenomena with unprecedented accuracy?
All of these now seem plausible, if still extremely challenging. That’s because the core of quantum information devices—known as a “qubit” in analogy to the “bit” of a conventional computer memory—has to be completely shielded from outside electrical or magnetic forces. Yet at the same time, to be useful, they have to be able to communicate with each other and share information with the outside world.
A qubit can take many forms. One example is a tiny ring in which a superconducting current flows one direction or another, forming a kind of artificial atom, which when cooled to the temperatures of liquid helium exhibits quantum phenomena. These superconducting artificial atoms have already proven useful for research into quantum physics, and their potential ease of manufacture and ability to operate at nano- second time scales make them a promising candidate for technology applications. Another form of qubit is a charged atom trapped in a
vacuum by rapidly oscillating electromagnetic fields. Still a third example of a qubit is a single photon of light trapped in a wave guide.
The technological challenge is in combining multiple qubits with methods of exchanging information between them, measurement and control techniques, and architectures for practical systems—in most cases, with the whole system kept at the temperature of liquid helium. But if that can be done—which seems increasingly likely—the unique properties of quantum systems offer tantalizing power.
Take encryption, for example. With one existing widely-used public key encryption system that depends on the difficulty of finding the prime numbers that compose a code, it would take years for today’s supercomputers to crack a code with 1000 binary digits; a quantum computer could do it in seconds. That’s because a quantum computer with, say, 10 qubits, ope- rates a bit like a parallel computer doing 1024 simultaneous computations; with 30 qubits, the number rises to a billion simultaneous computations; with 40 qubits, a trillion. So it doesn’t take a very large quantum computer to simply overpower some kinds of computational problems or to sort through even the most massive datasets. Scientists expect that more advanced quantum computers capable of broader applications might be possible within a decade.
There are large efforts underway in several countries to install and scale up quantum technologies that will allow a huge jump ahead in computing power and absolute security in long distance communications. U.S. leadership in these strategically important areas is not assured, especially given recent budget constraints.
Or take long-distance communications security. If two people want to send secret information over a public channel and they encrypt the message with a unique code, it’s usually impossible to break the code. But the weakness in any such communication system comes when the two parties try to share and agree on a code—which can be intercepted. With a quantum communications system that operated by exchanging qubits, however, any attempt to intercept the code alters the transmission—so the parties will know it’s been breached and won’t use it. With automated systems capable of generating and sending thousands of potential codes a second, and then selecting and using those that have not been tampered with, secure communications becomes possible. And the security depends not on the cleverness of a code, but on the peculiar physics of quantum systems that make it impossible to measure a quantum particle without also perturbing it. Both military and commercial secrets could stay secret.
Quantum information processing devices are also useful for precision measurement—the 2012 Nobel Prize in physics was awarded to scientists who had used techniques of quantum
information processing to construct devices that attained unprecedented precision in the measurement of time. Similar approaches are possible to measure electric charge, magnetic flux, heat flow, and other quantities. And just as with computational power, as the number of qubits in a device increase, so too will the ultimate limits of precision.
The field of quantum information science began in the United States, but there are now large efforts underway in several countries to install and scale up these technologies—in effect,
to install a new kind of quantum internet/ quantum cloud that allows communication and data storage with absolute security and very powerful solutions for certain types of computing problems. The Swiss are investing heavily in quantum communications. A Canadian company is producing the first commercial quantum information processing computer. Publications from Chinese scientists in this field are rising rapidly. So U.S. leadership is not assured, especially given recent budget constraints, while the potential outcomes seem quite important both strategically and commercially.