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Experiment confirms quantum theory weirdness

The bizarre nature of reality as laid out by quantum theory has survived another test, with scientists performing a famous experiment and proving that reality does not exist until it is measured.

Physicists at The Australian National University (ANU) have conducted John Wheeler’s delayed-choice thought experiment, which involves a moving object that is given the choice to act like a particle or a wave. Wheeler’s experiment then asks – at which point does the object decide?

Common sense says the object is either wave-like or particle-like, independent of how we measure it. But quantum physics predicts that whether you observe wave like behavior (interference) or particle behavior (no interference) depends only on how it is actually measured at the end of its journey. This is exactly what the ANU team found.

“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” said Associate Professor Andrew Truscott from the ANU Research School of Physics and Engineering.

Despite the apparent weirdness, the results confirm the validity of quantum theory, which governs the world of the very small, and has enabled the development of many technologies such as LEDs, lasers and computer chips.

The ANU team not only succeeded in building the experiment, which seemed nearly impossible when it was proposed in 1978, but reversed Wheeler’s original concept of light beams being bounced by mirrors, and instead used atoms scattered by laser light.

“Quantum physics’ predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” said Roman Khakimov, PhD student at the Research School of Physics and Engineering.

Professor Truscott’s team first trapped a collection of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them until there was only a single atom left.

The single atom was then dropped through a pair of counter-propagating laser beams, which formed a grating pattern that acted as crossroads in the same way a solid grating would scatter light.

A second light grating to recombine the paths was randomly added, which led to constructive or destructive interference as if the atom had travelled both paths. When the second light grating was not added, no interference was observed as if the atom chose only one path.

However, the random number determining whether the grating was added was only generated after the atom had passed through the crossroads.

If one chooses to believe that the atom really did take a particular path or paths then one has to accept that a future measurement is affecting the atom’s past, said Truscott.

“The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behavior was brought into existence,” he said.

The research is published in Nature Physics.

Source: ANU

A cartoon illustration of a levitated drop of superfluid helium. A single photon circulating inside the drop (red arrow) will be used to produce the superposition. The drop's gravitational field (illustrated schematically in the background) may play a role in limiting the lifetime of such a superposition.

Credit: Yale News

Opening a window on quantum gravity

Yale University has received a grant from the W. M. Keck Foundation to fund experiments that researchers hope will provide new insights into quantum gravity. Jack Harris, associate professor of physics, will lead a Yale team that aims to address a long-standing question in physics — how the classical behavior of macroscopic objects emerges from microscopic constituents that obey the laws of quantum mechanics.

Very small objects like photons and electrons are known for their odd behavior. Thanks to the laws of quantum mechanics, they can act as particles or waves, appear in multiple places at once, and mysteriously interact over great distances. The question is why these behaviors are not observed in larger objects.

A cartoon illustration of a levitated drop of superfluid helium. A single photon circulating inside the drop (red arrow) will be used to produce the superposition. The drop's gravitational field (illustrated schematically in the background) may play a role in limiting the lifetime of such a superposition. Credit: Yale News
A cartoon illustration of a levitated drop of superfluid helium. A single photon circulating inside the drop (red arrow) will be used to produce the superposition. The drop’s gravitational field (illustrated schematically in the background) may play a role in limiting the lifetime of such a superposition.
Credit: Yale News

Scientists know that friction plays an important part in producing classical behavior in macroscopic objects, but many suspect that gravity also suppresses quantum effects. Unfortunately, there has been no practical way to test this possibility, and in the absence of a full quantum theory of gravity, it is difficult even to make any quantitative predictions.

To address this problem, Harris will create a novel instrument that will enable a drop of liquid helium to exhibit quantum mechanical effects. “A millimeter across,” Harris said, “our droplet will be five orders of magnitude more massive than any other object in which quantum effects have been observed. It will enable us to explore quantum behavior on unprecedentedly macroscopic scales and to provide the first experimental tests of leading models of gravity at the quantum level.”

Game-changing research

The W.M. Keck Foundation grant will fund five years of activity at the Harris lab, which is part of Yale’s Department of Physics. In the first year, Harris and his team will construct their apparatus, and in subsequent years they will use it to perform increasingly sophisticated experiments.

“We are extremely grateful to the W.M. Keck Foundation for this generous support,” said Steven Girvin, the Eugene Higgins Professor of Physics and deputy provost for research. “This is a forward-looking grant that will advance truly ground-breaking research.”

Girvin, whose own research interests include quantum computing, described the Harris project as a possible game-changer. “Truly quantum mechanical behaviors have been observed in the flight of molecules through a vacuum and in the flow of electrons through superconductive circuits, but nothing has been accomplished on this scale. If Jack succeeds, this would be the first time that an object visible to the naked eye has bulk motion that exhibits genuine quantum mechanical effects.”

Into the whispering gallery

To explain his project, Harris invokes an architectural quirk of St. Paul’s cathedral, a London landmark with a famous “whispering gallery.” High up in its main dome, a whisper uttered against one wall is easily audible at great distances, as the sound waves skim along the dome’s interior. Harris plans to create his own whispering gallery, albeit on a smaller scale, using a droplet of liquid helium suspended in a powerful magnetic field. Rather than sound waves, Harris’ gallery will bounce a single photon.

This approach is closely related to an idea proposed by Albert Einstein in the 1920s, but until now, it has remained beyond the technical capabilities of experimentalists. To complete the experiment, Harris will need to combine recent advances in three different areas of physics: the study of optical cavities (objects that can capture photons), magnetic levitation, and the strange, frictionless world of superfluid helium. “Superfluid liquid helium has particular properties, like absence of viscosity and near-absence of optical absorption,” Harris explained. “In our device, a drop of liquid helium will be made to capture a single photon, which will bounce around inside. We expect to see the drop respond to the photon. “A photon always behaves quantum mechanically,” he added. “If you have a macroscopic object — our helium drop — that responds appreciably to a photon, the quantum mechanical behavior can be transferred to the large object. Our device will be ideally suited to studying quantum effects in the drop’s motion.” Potential applications for Harris’ research include new approaches to computing, cryptography, and communications. But Harris is most excited about the implications for fundamental physics: “Finding a theory of quantum gravity has been an outstanding challenge in physics for several decades, and it has proceeded largely without input from experiments. We hope that our research can provide some empirical data in this arena.”

About the W.M. Keck Foundation

The W.M. Keck Foundation was established in 1954 by William Myron Keck, founder of the Superior Oil Company. The foundation supports pioneering research in science, engineering, and medicine and has provided generous funding for numerous research initiatives at Yale University. In 2014, the Keck Foundation awarded a separate grant to a team of scientists led by Corey O’Hern, associate professor of mechanical engineering at Yale, to explore the physics of systems composed of macro-sized particles. Source : Yale News

Quantum computer as detector shows space is not squeezed

 Robert Sanders


 

Ever since Einstein proposed his special theory of relativity in 1905, physics and cosmology have been based on the assumption that space looks the same in all directions – that it’s not squeezed in one direction relative to another.

A new experiment by UC Berkeley physicists used partially entangled atoms — identical to the qubits in a quantum computer — to demonstrate more precisely than ever before that this is true, to one part in a billion billion.

The classic experiment that inspired Albert Einstein was performed in Cleveland by Albert Michelson and Edward Morley in 1887 and disproved the existence of an “ether” permeating space through which light was thought to move like a wave through water. What it also proved, said Hartmut Häffner, a UC Berkeley assistant professor of physics, is that space is isotropic and that light travels at the same speed up, down and sideways.

“Michelson and Morley proved that space is not squeezed,” Häffner said. “This isotropy is fundamental to all physics, including the Standard Model of physics. If you take away isotropy, the whole Standard Model will collapse. That is why people are interested in testing this.”

The Standard Model of particle physics describes how all fundamental particles interact, and requires that all particles and fields be invariant under Lorentz transformations, and in particular that they behave the same no matter what direction they move.

Häffner and his team conducted an experiment analogous to the Michelson-Morley experiment, but with electrons instead of photons of light. In a vacuum chamber he and his colleagues isolated two calcium ions, partially entangled them as in a quantum computer, and then monitored the electron energies in the ions as Earth rotated over 24 hours.

As the Earth rotates every 24 hours, the orientation of the ions in the quantum computer/detector changes with respect to the Sun’s rest frame. If space were squeezed in one direction and not another, the energies of the electrons in the ions would have shifted with a 12-hour period. (Hartmut Haeffner image)
As the Earth rotates every 24 hours, the orientation of the ions in the quantum computer/detector changes with respect to the Sun’s rest frame. If space were squeezed in one direction and not another, the energies of the electrons in the ions would have shifted with a 12-hour period. (Hartmut Haeffner image)

If space were squeezed in one or more directions, the energy of the electrons would change with a 12-hour period. It didn’t, showing that space is in fact isotropic to one part in a billion billion (1018), 100 times better than previous experiments involving electrons, and five times better than experiments like Michelson and Morley’s that used light.

The results disprove at least one theory that extends the Standard Model by assuming some anisotropy of space, he said.

Häffner and his colleagues, including former graduate student Thaned Pruttivarasin, now at the Quantum Metrology Laboratory in Saitama, Japan, will report their findings in the Jan. 29 issue of the journal Nature.

Entangled qubits

Häffner came up with the idea of using entangled ions to test the isotropy of space while building quantum computers, which involve using ionized atoms as quantum bits, or qubits, entangling their electron wave functions, and forcing them to evolve to do calculations not possible with today’s digital computers. It occurred to him that two entangled qubits could serve as sensitive detectors of slight disturbances in space.

“I wanted to do the experiment because I thought it was elegant and that it would be a cool thing to apply our quantum computers to a completely different field of physics,” he said. “But I didn’t think we would be competitive with experiments being performed by people working in this field. That was completely out of the blue.”

He hopes to make more sensitive quantum computer detectors using other ions, such as ytterbium, to gain another 10,000-fold increase in the precision measurement of Lorentz symmetry. He is also exploring with colleagues future experiments to detect the spatial distortions caused by the effects of dark matter particles, which are a complete mystery despite comprising 27 percent of the mass of the universe.

“For the first time we have used tools from quantum information to perform a test of fundamental symmetries, that is, we engineered a quantum state which is immune to the prevalent noise but sensitive to the Lorentz-violating effects,” Häffner said. “We were surprised the experiment just worked, and now we have a fantastic new method at hand which can be used to make very precise measurements of perturbations of space.”

Other co-authors are UC Berkeley graduate student Michael Ramm, former UC Berkeley postdoc Michael Hohensee of Lawrence Livermore National Laboratory, and colleagues from the University of Delaware and Maryland and institutions in Russia. The work was supported by the National Science Foundation.

Source: UC Berkeley

Fast, cheap, and under control

New book argues that inexpensive, employee-driven business experiments can help drive innovation.

By Peter Dizikes


CAMBRIDGE, Mass. – When it comes to prescription drugs, patient “compliance” is a concern: Are people, especially the elderly, taking their medication on the proper schedule? While pharmaceutical firms focus on the research and development of drugs, knowing more about patient habits might, at a minimum, help those firms make the case for the effectiveness of their products.

Perhaps, then, some firms could benefit from a few experiments designed to help them learn more about their end-users: low-cost interventions that might involve, say, giving customers the opportunity to provide useful feedback about their habits. Indeed, small-scale business experiments designed from within might be the most valuable innovation investments most organizations can make, according to a new book on the subject.

“The purpose of an experiment is not to solve the problem, but to generate insights,” says Michael Schrage, a research fellow at the MIT Sloan School of Management, and a member of the school’s executive education teaching faculty. Moreover, Schrage claims, some businesses may discover a kind of power law of experimental knowledge: “If you design your experiments [to be] simple, frugal, and fast, you frequently can capture 80 percent of the useful insights you need for 20 percent of the time and money you’re used to investing.”

Now in his new book, “The Innovator’s Hypothesis,” published this month by the MIT Press, Schrage fleshes out the idea of “5×5” experiments as a useful tool for business innovation: having a diverse team of five employees come up with five experiments that can be tested within five weeks, for under $5,000 each.

“I’m not saying, get rid of your planning, get rid of your analytics,” Schrage says. “But when you look at your portfolio of innovation options, you should have some sort of serious investment in fast, simple, cheap, scalable, experiments.”

Airline test cases

To be sure, the notion of the 5×5 experiment bears some relation to famous business practices of the past, such as Toyota’s effort to implement “continuous improvement” from within, or more recent tech-sector initiatives to give employees a portion of work time devoted to firmwide innovation. But Schrage wants to go beyond the incrementalism of continuous improvement.

In his book, however, Schrage focuses on the specific parameters of the 5×5 idea, contending that many business practices can be tested effectively, and relatively cheaply, using this specific model. For instance, the idea of persuading airline passengers to volunteer to be bumped from their flights, for compensation, he notes, dates to at least 1968, when an economist first suggested it — but the practice wasn’t widely implemented until the late 1970s. Small-scale tests could have shown the value and feasibility of the idea much sooner than that.

But for a specific 5×5 experiment to have value, Schrage notes, it needs to yield useful information, no matter what the result is. As Schrage describes in the book, he himself thought it would prove valuable for airlines to charge more to passengers who wanted to sit together in groups of more than two — but in online-booking tests, air travelers resist paying more for seats in order to be grouped together. Still, that’s a useful and practical piece of knowledge for airlines and travel companies to have.

In that vein, getting employees to see that their own ideas might not reach fruition, Schrage believes, may be the most difficult thing about getting the 5×5 method to take hold within a firm.

“It’s hard because people want their hypothesis to be the business plan,” Schrage says. “They want to prove their hypothesis. We’re just as interested if the hypothesis doesn’t test valid.”

To make the 5×5 effort work, Schrage also recommends that employees think specifically about which executives might be most receptive to certain innovations, or the experimental method as a whole, while trying to affect change at their firms. No innovation methodology, he believes, can escape corporate politics and culture.

“The not-so-hidden agenda [of the method] is to provide a new opportunity for alignment between the visions and aspirations of [executives] and the people who actually do the work and interact with clients and customers,” Schrage says. “It creates an opportunity to engage with top management.”

The general approach, Schrage thinks, can also improve a firm from within in other ways, by further tapping the insights and talents of a firm’s employees, and perhaps even help morale in the process.

“The real value isn’t just in terms of innovation portfolios,” Schrage asserts. “It’s in helping boost the human capital, the creativity, the innovative capacity of individuals who participate,” Schrage says.

Source : MIT News Office