Talk – Does God Play Dice With Angles?

27

ANNOUNCEMENT
Please feel free to forward this to interested friends and colleagues.

Science Centre Singapore

and

British High Commission, Singapore

cordially invite you

to

on

Monday, 15 October 2012
from 7:00pm to ~8:30pm

with

who asks

Does God Play Dice with Angles?
Please see below for more information.

in
The Newton Room
Science Centre Singapore.
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Attendance is free for those who pre-register.
Reservations are accepted on a first-come-first-served basis due to limited seating.
Please make your reservations by replying to kt_pang@science.edu.sg.
Please include your name, the number of attendees &
your Science Centre membership link number (if any).
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We will retain your e-mail address only so as to inform you of future Science Centre events.
If you wish to have your email address removed from our list, please inform us. Thank you.
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Does God Play Dice With Angles?

Towards the end of the 19th Century, many thought that science itself was almost complete – that all basic scientific knowledge that needed to be known was known. Then in 1905, Einstein published papers in 3 areas that shook the scientific world. Although Einstein’s relativity transformed the Newtonian universe, and his ideas of Brownian motion effectively supported the discrete, atomic theory of matter, it was his work on the photoelectric effect that actually won him the 1921 Physics Nobel Prize. Einstein’s explanation suggested that light was quantised and could, under the right conditions, behave like a stream of particles (photons), as well as a wave. Thus Einstein was responsible for fuelling the birth of a new Physics as well as one of the most successful theories ever – namely Quantum Mechanics (QM). Although this wave-particle duality of light seems odd, all scientists and philosophers have accepted it as an accurate model and description of the actual behaviour of light. However, the deeper implications of QM and this duality can be demonstrated by the simple Young’s double slit experiment in which a monochromatic light illuminating 2 narrow slits creates alternating bright-dark interference fringes on a screen. However, if the source intensity is reduced until single photons are released one at a time, the fringe pattern still persists. But how can/does a single photon (a particle) produce wave-like interference? Does the photon interfere with itself? After passing through the 2 slits (how? which one?), the single photon will land on any one of the bright fringes with roughly equal probability. Question: When does the photon decide which bright fringe to land on? …

Einstein believed that this “decision” was precisely determined by the initial conditions, even though some of the latter might be permanently hidden. Contrarily, Niels Bohr believed that random chance must produce various outcomes in any perfectly repeated experiment, ie the outcome was only decided at the instant of measurement-observation. Einstein’s response to this suggested role of random chance on the universe, was “God does not play dice with nature”. He co-wrote a 1935 paper with Podolsky and Rosen (EPR), explaining the paradox. Even though John Bell formulated an inequality to test the entanglement limit in the 1960s, this famous quantum paradox was only finally resolved in the 1980s after Alain Aspect completed a number of groundbreaking experiments by measuring the polarisation of 2 photons that had moved far apart after starting out (entangled) together. His experiments showed that their orientations were only decided at the moment of measurement, and that the measurement of any one photon instantaneously determined the state of the distant other. This quantum entanglement (QE), referred to as“spooky action at a distance” (Einstein) thus lends strong support to Bohr’s interpretation.  Entangled polarisation states have guaranteed secure communication systems to operate along optical fibres where the preservation of entanglement fundamentally confirms that no eavesdropper is listening.

Perhaps the most striking example of QE is “ghost diffraction”. In the 1990s, using one of 2 photon sources, Shih and co-workers showed that when a Young’s double slit was placed in one of the photon beams, interference fringes were observed simultaneously in the other. By measuring the position distribution of each photon as it passed through the slits, the distribution of the transverse linear momentum (conjugate variable) of the other was instantaneously defined. At Glasgow, we have just built a non-local ghost imaging system where the camera signal is obtained from light that has never interacted with the object.

In addition to linear momentum, our work concerns the angular momentum of light. In an analogy to ghost diffraction, we have shown that measuring the angular position of each photon defines the angular momentum of the other. It seems as if God does indeed play dice with angles and that this playing of dice enables both secure communication and new opportunities in remote imaging.

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Miles Padgett

… holds the Kelvin Chair of Natural Philosophy (Physics and Astronomy) and is the Dean of Research (Science and Engineering College Senior Management) at the University of Glasgow. He is Professor of Optics in the Department of Physics and Astronomy.

Funded by a combination of government, charity and industry, he leads a 15-person team covering a wide spectrum from blue-sky research to applied commercial development. His research group has published over 250 papers that have received over 7500 citations in the world’s leading scientific journals. He has made a number of TV and radio appearances and numerous public lectures, promoting science and technology to the widest possible audience.

He has also accorded many honours.
·         In 2001, he was elected to the Fellowship of the Royal Society of Edinburgh.
·         In 2007/8, he was a Leverhulme Trust, Royal Society Senior Research Fellow.
·         In 2008, he received the UK Institute of Physics, Optics and Photonics Division Prize for a “distinguished record of achievement in research that spans fundamental aspects of optical angular momentum and applied optical sensors”. From 2009, he holds a Royal Society/Wolfson Merit Award.
·         In 2009, Padgett was awarded the Institute of Physics, Young Medal “for pioneering work on optical angular momentum” being recognised for his studies in the field of optics and in particular of optical angular momentum. His contributions include an optical spanner for spinning micron-sized cells, use of orbital angular momentum to increase the data capacity of communication systems, and an angular form of the quantum Einstein-Podolsky-Rosen (EPR) paradox.
·         In 2011, he became a Fellow of the Optical Society.

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Science in the Café is Science Centre Singapore’s outreach platform to engage the public and those who find it easier to attend events after working hours. The science and scientific issues covered are wide-ranging – meant to whet the interests of various segments of the public. For more information, please view our webpages @http://www.science.edu.sg/events/Pages/sciencecafecalendar2012.aspx.

See you at the Science Centre.

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