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Research Areas
Quantum Optics
Laser cooling and trapping
Hybrid trapping of atoms and ions
Cavity Physics and Cavity QED
Electronically induced transparency (EIT)
Quantum walk of light
Light propagation in random
Fundamental tests of quantum mechanics
Quantum Information and Computing
Nonlinear Optics
Laser induced plasmas
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Quantum Optics
Quantum optics is a field of study in physics that applies quantum mechanical tools to understand phenomena involving light and its interaction with matter. Major fields of interest in quantum optics include manipulation of elemental particles like atoms, ions and molecules and the use of quantum optics to build further upon our current understanding of quantum information. Quantum coherence transfer between atoms and light and creation of new quantum states of light and matter are some of the other questions being actively pursued at the moment. For this purpose, experiments involving low-intensity probes for atoms prepared in a superposition state, and Quantum Non-demolition (QND) measurements of quantum superposition states have been designed.
Another line of quantum optics research in LAMP focuses on the creation and manipulation of quantum correlations, and their transfer from photons to material objects. These material objects range from being in a state which is gaseous, with a dilute collection of loosely bound atoms, to solid state objects which have micrometer dimensions like a micromechanical spring. A comprehensive study of photon-matter interactions within such a dynamic range in sizes and states of matter, is carried out to answer how quantum properties are created, stored and retrieved in such diverse systems. This research may also unravel fundamental constraints involved in creating quantum properties in matter with mesocopic dimensions, existing at room temperature. The prevalence of quantum effects in light and matter interaction has naturally led the LAMP group to explore some foundational questions in quantum mechanics. One such area of current interest is the area of Quantum measurements. Weak measurements and weak value amplifications in atom-photon interactions are being studied both theoretically and experimentally by the group.
Laser cooling and trapping
Laser cooling and trapping is a fairly novel technique that has gained huge popularity throughout the world of physics since the last decade. Presently, atoms can be cooled to extremely low kinetic temperatures (150 microK) and trapped for a time period of the order of seconds. There are some techniques to cool and trap atoms of alkaline elements, the most common one being Doppler cooling. In Doppler cooling, three mutually perpendicular laser beams are made to intersect at the centre of a chamber while a pair of magnetic coils produce a magnetic field that is zero at the centre of the chamber but increases radially outwards. Tuning the wavelength and polarization of the laser beams, atoms can be cooled by repeated absorption and emission of light, and trapped by an inward force arising out of the combination of the laser beams and the spatially varying magnetic field. Or in other words, Doppler cooling involves a Magneto Optical Trap (MOT). Electromagnetically induced transparency and related phenomena and nature of fluctuations in a collection of cold atoms are being studied at the Laser cooling lab.
Hybrid trapping of atoms and ions
A hybrid trap experiment is one which combines cold atoms, ions and molecules and studies their interaction to great accuracy. Research at RRI has overturned long held views on the nature of energy transfer in the interaction of trapped ions with trapped atoms. Collision rates between atoms and ions have been accurately measured. Ion molecule processes have also been investigated to show a rich variety of very interesting phenomena.
Cavity physics and Cavity QED
Hybrid trap experiments as mentioned above, can access the quantum electrodynamic regime for atom-electromagnetic field interactions. Using cold ions, atoms and molecules simultaneously cooled and trapped with photons in a high Q optical cavity, the non-classical nature of atom-field interactions are being tapped. This is the first such experiment of its kind and provides a complete system for the study of cold dilute classical and quantum gases.
Electromagnetically induced transparency (EIT)
EIT is a quantum mechanical phenomenon where, under specific conditions, an absorption line of a material can be cancelled, changing it from opaque to transparent at that particular frequency. EIT can be observed when two highly coherent lasers are tuned to interact with three or more quantum states of a material. A concerted effort is on at RRI to understand this phenomenon both from a theoretical and experimental point of view.
Quantum walk of light
Just as the mathematical formulation of a classical random walk is used in search algorithms where the search parameter is random, so also quantum walks, which are the equivalent of random walks in quantum computing, can be mathematically made to be a part of a quantum algorithm. The frequency space of quantum walks is currently being investigated by the LAMP group.
Light propagation in random media
Multiple scattering of light in random media, like fog, reduces visibility because propagation of light in random media is diffusive rather than ballistic. This in turn leads to some interesting phenomena like mirrorless lasing, Levy statistics and weak and strong localization. Experiments using colloidal suspensions of dielectric or magnetic microspheres, both active and passive, as well as Monte Carlo simulations and theoretical analyses are the different methods being employed to probe this process of light propagation.
Fundamental tests of quantum mechanics
Quantum mechanics is a cornerstone of modern physics. Just as the 19th century was called the Machine Age and the 20th century the Information Age, the 21st century promises to go down in history as the Quantum Age. However, can we really claim to fully understand quantum mechanical principles? How much do we really believe of what we know? Answers to such questions require us to revisit the fundamental postulates of quantum mechanics and perform precision theoretical and experimental investigations to come up with the right bounds. In the LAMP group, a part of the focus is to attempt such investigations using single light particles i.e. single photons as tools. Such tests carry a lot of importance in the current theoretical physics scenario where a lot of importance is being given to unification of quantum mechanics and general relativity. Such unification attempts would also be benefitted if one can have a more precise understanding of the principles involved in at least one of the theories i.e. quantum mechanics.
Quantum Information and Quantum Computation
The main thrust here is research on aspects of quantum information and quantum computation. The systems of choice are qutrits (three dimensional quantum systems), based on spatial degrees of freedom of the single photon. The LAMP Group has one of the first labs in the country to develop the technology of single photon sources based on spontaneous parametric down conversion in bulk non-linear crystals. The single photons and their various degrees of freedom are used to investigate aspects of quantum optics and quantum information.
Photons are massless, charge-less particles and as such perfect for communication purposes. In the near future, the LAMP Group wishes to enter the domain of quantum communication and develop both terrestrial and satellite based technologies.
Nonlinear optics
Nonlinear optical (NLO) transmission of materials finds applications in optical switches, optical limiters and saturable absorbers. Materials show tunable, enhanced characteristics in the nano phase, which can be very different from their properties in the bulk form. Optical nonlinearities of novel nanoparticles and nanocomposites are being investigated in the LAMP group. Ultrafast (100 fs) and short (5 ns) laser pulses are employed to identify features of nonlinearity in different time domains, employing the techniques of Z-scan, four wave mixing and pump-probe spectroscopy. In addition to demonstrating prototype NLO devices like mesoscopic nanocarbon based optical diodes, these investigations have also thrown new light into the role of lattice defects in determining the nonlinear absorption behaviour of novel materials like Graphene.
Laser induced plasmas
Plasma, the fourth state of matter, is routinely produced in the LAMP labs by irradiating suitable targets with powerful pulsed lasers. These plasmas which exist only for a few microseconds can be considered as short-lived stars, and their study is often called 'Laboratory Astrophysics'. Ultrafast laser produced plasmas ejected from metal targets irradiated in vacuum are found to contain electrons, ions, visible radiation, and high energy photons in the soft and hard X-ray regimes. Spectroscopic investigation of the plasma can be used to identify constituent elements of an unknown target. Temporal evolution of the plasma studied using time of flight techniques in the nanosecond regime gives information on the velocity and recombination rates of the constituent ions and electrons.