Nobel Prize winners Serge Haroche, left, and David Wineland, right. Credit: Haroche, © CNRS Photothèque/Christophe Lebedinsky
Today the Royal Swedish Academy of Sciences awarded the Nobel Prize in physics to American David J. Wineland and Serge Haroche of France, who pioneered two similar experimental techniques for observing and controlling systems of quantum particles. “The Nobel laureates have opened the door to a new era of experimentation with quantum physics by demonstrating the direct observation of individual quantum particles without destroying them,” said the academy in a press release. The physicists’ efforts, described as “bringing to life the wildest dreams of science fiction,” could make possible computers more powerful than any seen before.
To understand Wineland and Haroche’s achievement, it helps to understand the quantum theory of superposition as illustrated in a famous example called “Schrodinger’s cat.” Imagine a cat in a sealed box that contains a poisonous vial of gas that has only a 50 percent chance of killing it. Until the box is opened and the cat can be observed, it is both dead and alive; it is in what is called a superposition of states. That is, “there is no single outcome unless it is observed … [Schrodinger’s cat demonstrates] the apparent conflict between what quantum theory tells us is true about the nature and behavior of matter on the microscopic level and what we observe to be true about the nature and behavior of matter on the macroscopic level — everything visible to the unaided human eye.”
Such is the nature of quantum states. Particles can hold multiple states at once (such as energy, for example), and the resulting state will not be known until the system is observed. Wineland and Haroche designed and built quantum systems analogous to Schrondinger’s cat and were able to experimentally verify the probabilistic nature of their quantum systems. They developed experimental methods that isolated individual ions and atoms in order to manipulate their specific quantum states and directly test theoretical quantum mechanics.
While both scientists managed to circumvent the intrinsic paradox of the experiment (how can we measure something if disturbing it changes the nature of it?), they did so in different ways. Wineland and his team at the National Institute of Standards and Technology isolated individual ions in electromagnetic traps, used laser light to excite the ions into superposition states, and measured the rate at which each possible outcome occurred. Haroche reversed the role of light and atoms, using a mirrored cavity to trap particles of light, called photons, and carefully injected single atoms in the cavity to change the state of the atom.
Accessing and manipulating large arrays of individual superposition states of quantum particles could have a large impact on computing. Our current computers work based on switches, known as transistors, each containing two possible states: on and off. Due to phenomenon of superposition, quantum-based processors could have many programmable states, leading to much, much faster computational times. However, isolating more than several quantum switches at a time is extremely difficult, and a testament to the achievements of this year’s winners.
Kenneth Evans is a graduate intern for Kirstin Matthews, fellow in science and technology policy at the Baker Institute. He is working toward a Ph.D. in applied physics under Douglas Natelson, a professor of physics and astronomy at Rice University.