Negative Refraction of Visible Light

Harry A. Atwater (photo courtesy: Caltech)

In the online publication 'Science Express', applied physics researchers from California Institute of Technology, Henri Lezec, Jennifer Dionne, and Professor Harry Atwater, reported their success in constructing a nanofabricated photonic material that creates a negative index of refraction in the blue-green region of the visible spectrum. Their device makes visible light travel in the opposite direction and not refract or bend when passing from one material to another, like from air through water or glass.

Researchers in recent years have created materials with negative diffraction for microwave and infrared frequencies. These achievements have exploited the relatively long wavelengths at those frequencies--the wavelength of microwaves being a few centimeters, and that of infrared frequencies about the width of a human hair. Visible light, because its wavelength is at microscopic dimensions--about one-hundredth the width of a hair--has defeated this conventional approach.

The physicists of the Atwater group at Caltech came up with a clever new idea that if new optical materials could be constructed at the nanoscale level in a certain way, it might be possible to make the light bend at the same angle. The datails are complicated, but have to do with the speed of light through the material itself.

They employed a few ideas from the emerging field of work on 'plasmonics', in which light is "squeezed" with specially designed materials to create a wave known as a 'plasmon'. In this case, the plasmons act in a manner somewhat similar to a wave carrying ripples across the surface of a lake, carrying light along the silver-coated surface of a silicon-nitride material, and then across a nanoscale gold prism so that the light reenters the silicon-nitride layer with negative refraction.

The method could in principle be used to construct optical microscopes for imaging things as small as molecules, and even to create cloaking devices for rendering objects truely invisible (none of the previous ideas about 'invisible' cloak had to do with visible light!).

Reference:
"Negative Refraction at Visible Frequencies",
by Henri J. Lezec, Jennifer A. Dionne, Harry A. Atwater,
Science Express (online), Link to Abstract.
Will be published in the journal 'Science' on a future date.

Quantum Theory : 5 Needed Breakthroughs -- Stephen Adler

Stephen Adler with grandchild in 2004 (photo courtesy: Institute for Advanced Study, Princeton)

[Prof. Stephen Adler of the School of Natural Sciences at the Institute of Advanced Study, Princeton is a widely respected authority in the field of Quantum Theory.

During the long career starting with Ph.D work in 1964 from Princeton University, Prof. Adler
continued to make important contribution in the field of Elementary Particles, Quantum Field Theory and Foundation of Quantum Physics.
His recent works can be best described by citing the following classic books that he wrote on his various research projects:

-- ``Adventures in Theoretical Physics: Selected Papers with Commentaries '' (World Scientific Publishing, January, 2006)
-- ``Quantum Theory as an Emergent Phenomenon'' (Cambridge University Press, 2004).
-- ``Quaternionic Quantum Mechanics and Quantum Fields'' (Oxford University Press, 1995).

During his long career, he held many important positions. He was Divisional Associate Editor for Particles and Fields of Physical Review Letters and also the Chairman of the Division of Particles and Fields of American Physical Society. He was a member of the Editorial Board of Physical Review D and Journal of Mathematical Physics. He is a member of the 'National Academy of Sciences' and Fellow of 'American Physical Society', 'American Academy of Arts and Sciences' and 'American Association for the Advancement of Science'.

Prof. Adler received J.J. Sakurai Prize from American Physical Society in 1988. In 1998 he was awarded the Dirac Medal of the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy.

We thought it would be great to hear from Prof. Adler his choice of 5 most important breakthroughs that the Quantum Theory needs.
- 2Physics.com Team]

1. To understand why there are three families of quarks and leptons.

2. To understand the hierarchy problem - why the electroweak scale is so much smaller than the Planck scale.

3. To understand why the cosmological constant is so small.

4. To understand how to get a satisfactory quantum theory of measurement.

5. To reconcile relativistic quantum theory with general relativity.

Interferometric Detection of Gravitational Waves : 5 Needed Breakthroughs -- David Reitze

[In our ongoing feature '5-Breakthroughs' , today's guest is Prof. David Reitze of University of Florida, Gainesville.

Prof. Reitze is the newly elected Spokesperson of the LIGO Science Collaboration (LSC), a self-governing collaboration seeking to detect gravitational waves, use them to explore the fundamental physics of gravity, and develop gravitational wave observations as a tool of astronomical discovery. It includes scientists from the LIGO Laboratory as well as collaborating institutions from US, Australia, Germany, India, Japan, Russia, UK. The mission of LSC is to insure equal scientific opportunity for individual participants and institutions by organizing research, publications, and all other scientific activities. In fact, the March meeting of LSC on scientific collaborations between LIGO and the French-Italian group Virgo is starting tomorrow in Baton Rouge, Louisianna.

In the field of gravitational wave interferometry, Prof. Reitze's research activities spanned a wide range of topics crucial for successful operation and improvement of the sensitivity of interferometric detectors: Investigation of thermal lensing in passive and active optical elements; development of high power optical components; development of new interferometer topologies for next generation detectors; design, construction and operation of the LIGO interferometers.

Here we present the 5 important breakthroughs that the new Spokesperson of LIGO Science Collaboration (LSC) wishes to see in the worldwide effort for the detection of gravitational waves.-- 2Physics.com Team]

"In order from 'most possible in the near term' to 'most ambitious' are my five most important breakthroughs needed for gravitational wave astrophysics :

1) The direct detection of gravitational waves from astrophysical events such as the inspiral and merger phases of binary neutron star or black hole systems. Observations of these events will reveal significant astrophysical information about neutron stars and black holes, including their masses, spins, and the nature of strong-field gravity in regions of high space-time curvature. As a side wish, I would like to see the development of computational waveform templates for BH-BH collisions as well as supernovae waveforms.

2) Large scale interferometer implementations of quantum optical methods which circumvent the 'standard quantum limit' imposed by the statistics of photons. Such methods include but are not limited to the use of non-classical states of light, ponderomotive squeezing, and line-broadened cavities. Any of these methods would enable GW astrophysicists to improve the sensitivity of interferometers, resulting in an improved rate of detection for gravitational wave events. In order to make these techniques work, however, we would need to develop mirrors which possess lower thermal noise, so I would like to see that too!

3) The development of large scale interferometers underground to push the sensitivity of ground-based instruments below a few Hz. Placing interferometers even 100 m underground dramatically reduces the disturbances due to seismic motion and improves the detection efficiency and event rates for low frequency emitters such as 20-50 solar mass black holes.

4) The development of the Laser Interferometer Space Antenna. LISA will allow astrophysicists to look at even lower frequencies and observe high mass black hole collisions.

5) The observation of the residual gravitational wave radiation from the Big Bang. Unlike the cosmic microwave background, the observation of relic gravitational waves provides a direct snapshot of the universe at the moment of its birth (or about 10^-43 sec after). "

Life & Death of a Single Photon Observed

Michel Brune (photo courtesy: l'Ecole Normale Supérieure in Paris)

Nearly one hundred years after such a quantum phenomenon was predicted, a team of French physicists led by Michel Brune at the l'Ecole Normale Superieure in Paris has been successful in watching single photons appearing spontaneously from vacuum, live a brief life, and then vanish into the vacuum. The experiment is the best realization so far of "quantum non-demolition" (QND) measurements on single photons, whereby the presence of a photon is determined without destroying it.

The team used atoms to make a QND measurement of the quantum state of a system containing one photon. They used a microwave cavity cooled to 0.8K. In such a low temperature state, there is about a 5% chance that the cavity will be devoid of microwave photons and a 50% chance that a single photon can be found inside the cavity. The single photon can spontaneously appear from the vacuum and may vanish in less than one second.

A stream of rubidium atoms is passed though the cavity. These have an electron in a highly excited state (so called Rydberg atoms) and are very sensitive to external perturbations, such as electric fields. The atoms are prepared such that they can exist in one of two quantum states (“g” and “e”). The atoms are flipped between g and e by a non-resonant interaction with the cavity field. If the atoms cross an empty microwave cavity, most of them will emerge in state 'g', whereas if they encounter a photon the majority will emerge in state 'e'.

The photon, when it gets absorbed, displaces the position of the atomic energy levels of such a Rubidium atom. As the atoms emerge from the cavity, their state is determined using a high resolution spectroscopy. The team was thus able to make hundreds of such measurements on a single photon without destroying it. And that's the way they succeeded in watching a single photon emerge from the vacuum, live a short life of less than one second, and then disappear.

The researchers are hopeful that their technique can also find a way into potential applications in quantum information systems, in which the cavity can assume the role of a logic gate that switches the quantum state of the atoms depending on the presence or absence of a single photon.

Reference
"Quantum jumps of light recording the birth and death of a photon in a cavity",
Sébastien Gleyzes, Stefan Kuhr, Christine Guerlin, Julien Bernu, Samuel Deléglise, Ulrich Busk Hoff, Michel Brune, Jean-Michel Raimond and Serge Haroche,
Nature, Volume 446, Number 7133, p297 (15 March, 2007)

Interferometric Detection of Gravitational Waves: 5 Needed Breakthroughs -- Seiji Kawamura

[ In our ongoing feature '5-Breakthroughs', so far most of our guests were from the exciting field of research on detection of gravitational waves. It started with David Shoemaker of LIGO and we also had Jean-Yves Vinet from French-Italian Virgo project and David Blair of the Australian effort, AIGO. Our today's guest is Prof. Seiji Kawamura of the Japanese endeavor, TAMA.

Seiji Kawamura is an associate professor at National Astronomical Observatory(NAO) at Mitaka, Tokyo, Japan. He was involved in joint Caltech-MIT LIGO project from its early days and worked on the 40m prototype interferometer (at Caltech), suspension system, and advanced R&D for the LIGO project between 1989 and 1997.

In 1997 he joined the TAMA project, the Japanese 300 meter interferometer for the detection of gravitational waves. As the leader of the detector group, he could lead TAMA to attain the world-best sensitivity at that time.

In addition he initiated and has been in charge of the resonant sideband extraction experiment, quantum non-demolition experiment, super-high frequency gravitational wave detection, and displacement-noise-free interferometer. He also leads the Japanese space gravitational wave antenna DECIGO.

Here is Seiji's list of 5 breakthroughs he would like to see in the ongoing worldwide effort to detect gravitational waves using interferometric antennas.
-- 2Physics.com Team]

"- homodyne detection with ponderomotive squeezing to suppress radiation pressure noise

- high-power laser to suppress shot noise

- cryogenic mirror/suspension to suppress thermal noise

- interferometer in space to remove seismic noise and to enhance gravitational wave signals

- displacement-noise-free interferometer to cancel all kinds of displacement noise"

High Energy Physics: 5 Needed Breakthroughs -- Barry Barish

[Our today's guest in the ongoing feature '5 Breakthroughs' is Prof. Barry Barish (photo courtesy: Caltech).

Barry Barish is a Linde Professor of Physics, Emeritus at the California Institute of Technology, where he taught and conducted research since 1963. He is also the Director of the Global Design Effort for the International Linear Collider.

One of Prof. Barish's noteworthy experiments was at Fermilab using high energy neutrinos to reveal the quark substructure of the nucleon. These experiments were among the first to observe the weak neutral current, a linchpin in the Eletro-Weak unification theory of Glasgow, Salam and Weinberg.

In 1980s Prof. Barish led an international effort to build a sophisticated underground detector (MACRO) in Italy to search for magnetic monopole and solve other related problems in the emerging field of particle astrophysics. The experiment provided the best limits for the Grand Unified magnetic monopoles and some of the key evidences that neutrinos have mass.

In 1994, Prof. Barish became Principal Investigator of the joint Caltech-MIT LIGO project for the detection of gravitational waves and later became Director of the Laboratory from 1997 to 2005.

In 2002 he was nominated to the National Science Board that helps oversee the National Science Foundation (NSF) and advises the President and Congress on policy issues related to science, engineering and education. In 2002 he received the Klopsteg award of the American Association of Physics Teachers (AAPT) and was elected to the National Academy of Sciences. In 2003, he served as a member of the special panel for NASA that considered the future of the Hubble Space Telescope and the transition to the James Webb Space Telescope. Prof. Barish also served as co-chair of the subpanel of the High Energy Physics Advisory Panel (HEPAP) that developed the long-range plan for high energy physics in USA.

Here is Prof. Barish's list of 5 breakthroughs that he would like to see in high energy physics.
-- 2Physics.com Team]

"5 most important breakthroughs that are needed for particle physics:

1) Understanding what is the dark energy in the universe? (We don't even have a good idea here)

2) What is the dark matter? (This is the other big unknown, but at least we have some handles. We know it is non-baryonic and evidence points to either supersymmetric particles, or maybe axions. Perhaps it is neither)

3) What causes mass? (We have a very successful theory of particle physics, but the particles are massless. We need to understand the source of mass. The leading idea is that it is the Higgs mechanism, and we need to see if there is a Higgs particle or variant to make the next step. The Large Hadron Collider at CERN should answer this question)

4) Is the neutrino its own antiparticle? (This is a puzzle going back to Fermi and perhaps the next generation of experiments will resolve it by looking for neutrino-less double beta decay)

5) Is there ultimate unification of the forces of nature? (This is a long term intriguing simplification on our understanding of particles and fields, but present data does not support it. However, if there is a new symmetry in nature (supersymmetry) it could bring this unification.

These are all questions and there is hope we will have much better understanding within a decade or two."

Limit on Size of Dark Matter Clumps

Joseph Silk (photo courtesy: Oxford University)

Considering that the theory of gravitation is correct, when cosmologists analyze various observed data of our universe, they arrive at an intriguing observation -- that there's not nearly enough visible matter to hold the universe together. In fact, up to 95% appears to be missing.
The idea of the existence of dark matter originates from this. 'Dark matter' is supposed to be that illusive mass that remains invisible to modern day telescopes because it does not interact strongly with electromagnetic waves.

According to the model agreed upon by most physicists so far, dark matter could exist either as an accumulation of as-yet unseen 'weakly interacting massive particles' (WIMPs), or large clumps of 'massive compact objects' (MCOs) that do not emit any observable amount of radiation – or even as a mixture of both types.

Now Benton Metcalf from the Max Planck Institute for Astrophysics in Germany and Joseph Silk from the University of Oxford in the UK have attempted to see just how large these MCOs can be. They analysed the light from a supernovae five billion light years away. If an MCO had been there near the path of one of these light beams, the light would be undergo a measurable amount of dispersion by the MCO's gravitational field in an effect known as "gravitational lensing".

Because of the long path the light took to arrive the earth, the chances of a large MCO straying through would have been fairly high. But even after ploughing through data collected from almost 300 supernovae, the scientists could not find any dispersion caused by possible MCOs larger than one-hundredth the mass of the Sun. This implies that there is an 89% certainty they do not exist at all. Moreover, the physicists claim that MCOs larger than one-tenth the mass of the Earth can be confidently "eliminated" as the sole constituent of dark matter.

Until now many cosmologists believed in the existence of faint stars, neutron stars and black holes as significant constituents of dark matter. This result comes as a shock to those ideas. According to the recent Physical Review Letters paper by Metcalf and Silk, dark matter is more likely made of WIMPs.

Reference:
R. Benton Metcalf and Joseph Silk, "New Constraints on Macroscopic Compact Objects as Dark Matter Candidates from Gravitational Lensing of Type Ia Supernovae", Phys. Rev. Lett. 98, 099903 (E) (2007). Link to Abstract

Chiral Liquid Splits Light Beam

Ambarish Ghosh and Peer Fischer of the Rowland Institute at Harvard University with a microfluidic chiral detector

Imagine placing a spoon in a glass of iced-tea. The spoon will appear bent at the surface of the liquid, as the light that hit the spoon refracts when it travels from the liquid to air. Now imagine adding some sugar to the tea and according to a 200 year old prediction by Fresnel, you should see two spoons instead of one! The double image has its origin in the molecular structure of the sugar.

Fresnel was the first to suggest that light can be circularly polarized and that the difference in refractive indices between the left- and right-circularly polarized components underlies the optical rotation that is observed in sugar solutions. Sugar molecules are chiral, that is, they lack mirror-image symmetry, and they can in principle exist in either “right” or “left” handed configurations. However, almost all naturally occurring sugars are right-handed. Similarly, DNA, amino-acids and proteins are all of one hand. Adding the right-handed sugar molecules to the iced-tea changes the symmetry properties of the liquid, as it now becomes chiral too. The liquid is no longer described by a single refractive index, but by two refractive indices: one for left- and one for right-circularly polarized light.

Fig. 1: (a) Experimental setup to observe the refractive splitting of light in a chiral liquid.
(b) CCD image of the split beams as they traverse respectively 8, 12, 16, and 20 interfaces.

Given that there are two refractive indices, Fresnel predicted that a light beam refracting into or out of a chiral liquid will not only bend, but should also split into its two circularly polarized components [1]. That this phenomenon has gone unnoticed for so long is easily explained by the smallness of the splitting. The difference in the refractive indices for the two circularly polarized light components is typically less than a few parts in a million, and so the separation between the two images is expected to be extremely small. Nevertheless, Ambarish Ghosh and Peer Fischer from the Rowland Institute at Harvard have recently succeeded in imaging the splitting of a light beam in a chiral liquid [2]. The two physicists sent a laser beam through a stack of prismatic liquid cells filled alternately with chiral liquids such that at each interface the separation between the circular components increased until a double image could be clearly seen on a CCD camera. This is shown in the adjoining figure along with the experimental setup.

Ghosh and Fischer also closely examined what happens to a light beam that reflects inside a chiral liquid. In their recent paper in Physical Review Letters [2] they show that the “law of reflection” does not apply for liquids that lack mirror-image symmetry. The circularity of light reverses at a mirror and so the light beam experiences a different refractive index upon reflection. It follows that the angle of reflection does not equal the angle of incidence in liquids with handed molecules.

Compared to optical rotation, which requires liquid cells with long path-lengths, the refractive and reflective splitting of light should be much better suited to detect chirality in minute liquid volumes, since it occurs directly at the interface. The group is exploiting this advantage and is currently working on a chiral detector that will require only a few nanoliters of liquid (see figure). In a recent set of experiments the Harvard team also demonstrated that a magnetic field can cause a light beam to split [3] in a similar fashion to that observed in chiral liquids.

References:
[1] A. Fresnel, Ann. Chim. Phys. 28, 147 (1825).
[2] A. Ghosh and P. Fischer, "Chiral Molecules Split Light: Reflection and Refraction in a Chiral Liquid", Phys. Rev. Lett, 97, 173002 (2006). Link to Abstract
[3] A. Ghosh and P. Fischer, "Observation of the Faraday effect via beam deflection in a longitudinal magnetic field" . Preprint: http://arxiv.org/abs/physics/0702063

Upcoming Physics Conferences

Here is a selected list of forthcoming conferences in Physics. You are welcome to freely advertize Physics jobs or conferences in 2Physics by sending an email to 2Physics@gmail.com.

March 5-9: Foundations of quantum theory "special focus session" on foundations of quantum theory at the APS March Meeting (Denver, CO)
March 12-16: Nano and giga challenges (Tempe, AZ)
March 16-17: 23rd Pacific Coast Gravity Meeting (Caltech, Pasadena)
March 23-April 3: Quantum Gravity School (Zakopane, Poland)
March 24-29: The origin of galaxies (Otz Valley, nr. Innsbruck, Austria)
March 26-31: X hadron physics (Florianopolis, Brazil)
March 26-31: Nuclear Physics in Astrophysics (Dresden, Germany)
April 10-13: BICOS 2007 -- Bilbao Encounter On New Standard Cosmology (Bilbao, Spain)
April 23-27: Advanced computing and analysis techniques in physics (Amsterdam, The Netherlands)
May 10-12: The Hunt for Dark Matter: A Symposium on Collider, Direct and Indirect Searches (Fermilab, Batavia, IL)
May 12-16: Black Holes VI (White Point Resort, Prince Edward Island, Canada)
May 14-17: Origins of dark energy: conference and workshop (Hamilton, Canada)
May 14-18: Dark side of the universe (Villa Olmo, Italy)
May 14-18: Intl workshop on quantum noise (Caloundra, Australia)
May 18-20: 12th Canadian Conference on General Relativity and Relativistic Astrophysics (Fredericton, New Brunswick, Canada)
May 18-20: Workshop: excursions in the dark (Waterloo, Canada)
May 20-26: Matter and Energy in the Universe: from nucleosynthesis to cosmology (Chateau de Blois, France)
May 28-June 22: Theoretical advanced study institute (TASI) in elementary particle physics: "String Universe" (Boulder, Colorado, USA)
June 1-5: Central European workshop on quantum optics, 14th edition (Palermo, Italy)
June 4-7: 6th intl conference on nuclear and radiation physics (Almaty, Kazakhstan)
June 5-9: Annual APS Division of Atomic, Molecular and Optical Physics Meeting (Calgary, Canada)
June 10-13: From Quantum to Cosmos II -- Space-based Research in Fundamental Physics and Quantum Technologies (Bremen, Germany)
June 10-13: Intl conference on quantum information (Rochester, NY)
June 11-22: Summer school on particle physics (Trieste, Italy)
June 11-29: Physics at TeV colliders (Les Houches, France)
June 16-20: 4th intl workshop on quantum chromodynamics - theory and experiment (Bari, Italy)
June 18-20 SciNeGHE07: Fifth Workshop on Science with the New Generation of High Energy Gamma-ray Experiments (Villa Mondragone, Frascati, Rome, Italy)
June 18-22: School on attractor mechanism (Frascati, Italy)
June 22-July 3: 19th Petrov school -- summer school-seminar on recent problems in theoretical and mathematical physics (Kazan, Russia)
June 26-29: Physics in collision symposium on elementary and astro-particle physics (Annecy, France)
July 2-27: ESF school of theoretical physics: string theory and the real world (Les Houches, France)
July 8-14: 7th Edoardo Amaldi Conference on Gravitational waves (Sydney, Australia)
July 13-17: 'Cosmology and Strings' Workshop (ICTP, Trieste, Italy)
July 26-August 1: 15th intl conference on supersymmetry and the unification of fundamental interactions (Karlsruhe, Germany)
July 30-August 11: Cosmology and particle physics beyond the standard models (Cargese, France)
August 16-18: 11th Paris cosmology colloquium (Paris, France)
August 23-29: 13th Lomonosov conferences on elementary particle physics (Moscow, Russia)
September 2-6: Photons, atoms, and qubits (Royal Society, London, UK)
September 3-7: 3rd intl conference on physics and control (Potsdam, Germany)
September 2-7: Quantum Field Theory (Leipzig, Germany)
September 11-14: Recent advances in quantum integrable systems (Annecy-le-Vieux, France)
September 24-28: 6th intl Heidelberg conference on dark matter in astro & particle physics(Sydney, Australia)
October 1-5: Planets to Dark Energy (Manchester,UK)
October 11-13: Algebra, geometry, and mathematical physics (Göteborg, Sweden)
October 28-November 2: 7th intl conference on complex systems (Boston, MA)
November 4-10: Noise, information and complexity at quantum scale (Erice, Sicily, Italy)
December 4-9: Intl conference on magnetic materials (Kolkata, India)