Quantum Computing: The Search for Schrödinger’s Cat

Stephen DeAngelis

April 15, 2014

“Quantum computing may well represent the biggest breakthrough in computer technology since the invention of the microprocessor,” writes Lev Grossman. “Taking advantage of bizarre effects like quantum superposition and quantum entanglement, quantum computers have the potential to unlock massive amounts of processing power, and to solve problems that would take conventional computers literally centuries.” [“Quantum Computing: A Primer,” Time, 7 February 2014] The most important word in that last sentence is “potential.” The definition of “potential” is “having or showing the capacity to become or develop into something in the future.” The big question is: When will that future arrive? Understanding the physics behind quantum computing is not easy. As Grossman writes, “You could spend centuries trying to master the intricacies of quantum physics … or you could watch this video, which explains it all in about two minutes.”

The video talks about the D-Wave quantum computer around which swirls a lot of controversy. To learn more about the D-Wave computer, read my post entitled “Has the Age of Quantum Computing Finally Arrived?” One thing that isn’t controversial is the belief that if a fully operable quantum computer is built, it could change the world. As Eric Limer writes, “Someday, somehow, quantum computing is going to change the world as we know it. Even the lamest quantum computer is orders of magnitude more powerful than anything we could ever make today. But figuring out how to program one is ridiculously hard.” [“Why Programming a Quantum Computer Is So Damn Hard,” Gizmodo, 23 August 2013] Frankly, for most people understanding quantum computing is probably as “ridiculously hard” as learning to program one because it is difficult to imagine that something can be opposite things at the same time. The physicist Erwin Schrödinger probably offered the most famous analogy of this phenomenon when discussing his cat — which, he claimed, in the quantum world, could be both dead and alive. Anjana Ahuja reports that on one office door at the European Organization for Nuclear Research (Cern) in Switzerland, there is a poster featuring the photograph of a cat that proclaims,” “Lost cat. Please return dead and alive to Erwin Schrödinger.” [“The quantum realm is and is not the future of computing,” Financial Times, 9 February 2014]. Ahuja explains:

“The cat – a feline in a locked box that is both dead and alive until the box is opened – was a thought experiment devised by physicist Schrödinger to expose the counterintuitive weirdness of quantum theory. The theory posits that an entity can exist simultaneously in any number of states until the point at which it is observed, whereupon it will ‘collapse’ into one state – either purring or deceased in the case of the trapped tabby, which is incarcerated with a poison that either has or has not been released through radioactive decay. Geniuses have spotted that tapping into the quantum realm could release fantastic amounts of computing power.”

Despite the fact that constructing a quantum computer remains a challenging task, researchers continue to put together pieces of the puzzle. Recently researchers have developed more potential components for such computers. Scott Wasson reports, “A pair of research teams at the Max Planck Institute in Germany and Harvard University have demonstrated a new type of quantum logic gate and switch that could form the basis of quantum computers, according to this report at Popular Mechanics. The big advance, it seems, is establishing a reliable way to put a rubidium atom into the mind-bending state of superposition, where it is both ‘on’ and ‘off.’ Not only that, but the researchers have managed to create a mechanism for propagating this state to photons and having them share their state in common via quantum entanglement. These mechanisms could someday form the basis for a quantum computer, although scaling these things up to a sufficiently large scale is well beyond our current capabilities.” [“Researchers demo new method of creating quantum logic,” The Tech Report, 11 April 2014] Reporting on these developments, James Maynard indicates that these research breakthroughs may help address one of the crucial challenges involved in creating a quantum computer — the fragility of a superpositioned qubit. [“Flip the ‘switch’: New method makes quantum computing possible,” Tech Times, 12 April 2014] Maynard reports that Vladan Vuletić from MIT, and co-author of the paper, stated when announcing the breakthrough, “This is a major advance of this system. We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom.” Maynard continues:

“The strange qubit state is extremely fragile, providing challenges to quantum computing. Traditional devices needed to be kept extremely cold, requiring large mechanisms to maintain. Placing several qubits in close proximity can cause them to collapse into a more stable spin state. The new technology could provide a way of stabilizing quantum processors. ‘We expect our experiment to enable various applications,’ Max Planck Institute researchers wrote in the article detailing their investigation into quantum gates, including scalable quantum computation and quantum communication.”

Peter Dizikes adds, “The scientists believe their technique will allow them to increase the number of useful interactions occurring within a small space, thus scaling up the amount of quantum computing processing available.” [“New ‘switch’ could power quantum computing,” Phys.org, 9 April 2014] If all of this sounds a bit confusing or remarkable, you’re not alone. Dizikes reports, “If the research techniques seem a bit futuristic, Vuletić says that even as an experienced researcher in the field, he remains slightly awed by the tools at his disposal. ‘For me what is still amazing, after working in this for 20 years,’ Vuletić reflects, ‘is that we can hold onto a single atom, we can see it, we can move it around, we can prepare quantum superpositions of atoms, we can detect them one by one.'” You must admit that it is satisfying to see a scientist admit that he still admires the wonders of science.

The researchers discussed above are the not only scientists working on solving the quantum computing challenges. The University of Chicago reports:

“University of Chicago researchers and their colleagues at University College London have performed a proof-of-concept experiment that will aid the future development of programmable quantum computers. Many complex problems are difficult and slow to solve using conventional computers, and over the last several years, research has grown steadily toward developing quantum computation. In particular, optimization problems such as the ‘traveling salesman’ problem, which calculates the shortest possible route needed to visit a set of towns, become intractable as the number of towns grows. A quantum computer would exploit effects on the atomic and molecular scales to solve such problems dramatically faster than conventional computers. Recently a first generation of specialized computers has become available — with a new architecture that exploits quantum mechanics to help solve problems akin to the traveling salesman problem, with up to a few hundred towns. In a study published in the Proceedings of the National Academy of Sciences, a team from the James Franck Institute at UChicago and the London Centre for Nanotechnology at University College London describes an experiment that was performed on a crystal containing trillions, rather than hundreds, of quantum mechanical spins, which replicates some of the features of the current generation of much smaller, specialized computers. … Applied to practical and programmable quantum optimization computers, the results imply that quantum optimizers could obtain different solutions to problems such as the traveling salesman problem, when compared with conventional techniques. The research team concluded that these findings would affect both the design and use of quantum optimization systems.” [“Researchers bolster development of programmable quantum computers,” Science Codex, 10 April 2014]

It would appear that we are getting ever closer to finding Schrödinger’s cat. We’ll just have to wait until we can open the quantum computing box to find out whether the poor thing is going to dead or alive. For now, it remains both.