Views
From Physlab.lums.edu.pk
Spin Effects in Condensed Matter Systems and Opto-spin physics
Establishment of Quantum Optics Laboratory
| The immediate goal of this project is the establishment of an optics laboratory that can become a test bed for quantum effects such as single photon and multiple photon interference, photon antibunching, quantum teleportation and quantum key distribution, optical computing and quantum information processing. This will be a seed grant that will enable me to explore research directions in this area but in the near future, the lab will serve as a quantum mechanics laboratory for our undergraduate students. |
Entanglement in Macroscopic Magnetic Systems
| This is a theoretical project that also involves simulation and modeling. With the rapid progress in magnetic materials, comes the urge to explore magnetic spin systems that exhibit stronger-than-classical-correlations. There is considerable interest in looking for hotter and larger systems exhibiting entanglement. With this in mind, we are investigating spin coupling topologies, strengths of applied magnetic fields, asymmetries in applied fields, magnitudes and signs of coupling constants to look for regimes where one can hope to find entanglement at room temperature. This work ties in with the appropriate quantification measures for entanglement in multi-spin systems. |
Magneto-optical phenomena
| Faraday rotation describes a magneto-optical phenomenon i.e, interaction of optical radiation and magnetic field. It is the rotation of plane of polarization of linearly polarized monochromatic light transmitting through an optically inactive medium under the action of an axial magnetic field and is usually very small in magnitude, of the order of micro radians so, a large dc magnetic field is usually required. However, with the help of lock-in technique using the small ac magnetic field, this requirement can be bypassed. We have devised an experiment using the phase sensitive technique to study the Faraday rotation in different materials. We have also adapted this system to look at reflections, the experiment is the typical magneto-optical Kerr effect. Measurements have been performed investigating reflections from thin nanomagnetic layers. The ultimate goal is to use Kerr rotations to probe the spin structure of materials, notably the spin Seebeck and spin Hall effects. |
Synthesis of patterned magnetic films by electrodeposition
| Electrodeposition is the application of a metal coating to metallic or other conducting surface by an electrochemical process. It is well established technique for atomic layer growth of magnetic films. We are developing an electrochemical cell for patterned nano-magnetic film synthesis for use in our magneto-optical and spin calitronic applications. |  |
Spin caloritronics
|
The spin Hall effect is the spin analogue of the famed Hall effect, a spin voltage (difference in Fermi levels for oppositely polarized spins) develops across a current-carrying conductor. The spin accumulation should be detectable by the differing interaction of circularly polarized light with opposite spins. Similarly, we also have the spin Seebeck effect which uses a temperature gradient to induce the spin voltage, similar to the traditional Seebeck effect taking place in thermocouples, where a temperature difference produces an electrical voltage. The origin of both of these effects lies in the spin-orbit interaction. The magneto-optical characterization of these spin-dependent processes requires careful control, generation and detection of light polarization, controlled heating and precise temperature measurement, vacuum production and low-temperatures. We have, in our lab, acquired sufficient expertise in all of these areas individually and are now in a position to integrate our preliminary investigations. (For the low temperature studies, we have acquired a custom designed optical cryostat.) Traditionally, these so-called spin caloritronic effects are measured by electrical means. The electrical methods require cumbersome electrical connections and one is limited by the electrical noise of the system, the weak detected electrical signals may be overwhelmed with the intrinsic noise processes. The optical detection bypasses this limitation, thanks to very sensitive photon detectors which have high sensitivities (output current/incident light intensity). The final goals of this project are the:
|
  |
Supercapacitors
| We are working on a project that investigates high-k dielectric materials for supercapacitor applications. These materials are in fact nanoparticles grown in-situ on fibrous structures such as paper or cellulose. We are devising not only the complete theory and modeling of the interfacial polarization effects that cause the enhanced dielectric strengths, but have also developed a complete dielectric measurement system for this purpose. |  |
Development of Thermoelectric oxides for renewable energy conversion technologies
| This research project aims at developing perovskite based oxide materials that are stable and thermoelectrically efficient at the high temperatures common in Pakistan. I am developing analytical techniques for characterizing the properties of these materials, notably thermoelectric coefficient, thermal and electronic conductivities. |  |
Concomitant gradients in low field magnetic resonance imaging
| This research thesis discussed the issue of concomitant gradients that appear while doing MRI at low or zero fields. The origin of these gradients lies in the applicability of Maxwell’s equations and leads to distortions in acquired images. These distortions were quantitatively investigated. |
Optimization of NMR pulse sequences for quantum information processing
| The research work involved the development of the gradient ascent algorithm for finding optimal pulse sequences. The goal was to construct high fidelity, short in duration and low power sequences, keeping in mind the robust operations required for quantum computing. |
Biophysics
Compact hyperpolarized NMR and MRI
| There has been considerable progress in the invention and refinement of low-field and zero-field magnetic systems. In our research group, we are developing a compact and mobile spin polarizer to augment a benchtop NMR/MRI apparatus that is currently under development in the lab. This will enable the miniaturization of both the NMR and hyperpolarization mechanisms. |  |
|
Polarized, miniaturized and mobilized magnetic resonance can revolutionize the applicability of this widespread technique, extending it to developing countries, on-field inspections and testing, ambulatory medical care in disaster-struck areas, and the chemistry lab benchtop or the fume hood. For example, the high polarizations achieved from para-hydrogen enable us to detect trace amounts of chemical species and image their spatio-temporal profile, circumventing the low sensitivity issue plaguing NMR. In addition, the polarized para-hydrogen can be used as a magnetization storage vector for portable, mobile MRI instrumentation. It is known that the storage time can be extended beyond the conventional T1 times by exploiting the symmetry properties of the quantum singlet state. Such a long-lived and transferrable polarization agent can be achieved, for example, by the endohedral hydrogen fullerene, H2@C60 which is a molecule capable of surviving high temperature conditions (~500 deg C) for extended periods of time (~10 min). We are studying the use of endohedral fullerenes for the hyperpolarization storage and physical migration of the polarized product from one spatial location to another. Another experiment we will design, once our hardware is completely ready, is the in-situ and real-time study of polymerization reaction catalyzed by supported catalysts. The goals of this project include:
|
Microfluidic real-time pocket-sized PCR
| The Polymerase Chain Reaction (PCR) is a very important tool for medical diagnostics and finds applications in genomic analysis, infectious diseases detection, mutation studies and forensics. Available PCR machines are expensive, and the real challenge is to make them pocket sized and low cost, bringing them within reach of Pakistani clinical laboratories. In PCR, we amplify DNA using a thermocycling process, which involves three steps including Denaturing (at 95C), Annealing (50-60C) and Extension (72C). We have used TO-220 pacakaged BJT and FET for heating purposes. The temperature at each zone is controlled by LabVIEW based PID Controller. Real time analysis will be performed by optical means. |  |
Audiometric Measurements
| Pure tone audiometry is one of the most widely employed technique to measure the degree of hearing loss. In this method, the subject is provided with the pure tones of different frequencies and the audiometer measures the hearing level threshold at the specified frequencies. The difference from the standard threshold determines the level of hearing loss in humans. We are using a signal generator and headphones for pure tone audiometry. The experimenter changes the frequencies and the intensities using the signal generator and the measured voltage threshold values are converted into SPL. The test is performed for both left and right ear individually. The other part of the test involves masking one ear while testing the other ear. We are using bandlimited white gaussian noise as a making signal. We are currently performing the air conduction test, which in turn is used for the diagnosis of outer and middle air diseases. |  |
Physiological Measurements Kits for Technologists
| The SSE Physlab is developing a low-cost unit that will teach students the technology behind the scenes in physiological measurements. Pulse oximetry and ECG units have already been demonstrated and new experiments are being added to the reportoire. |  |
General Physics
Investigating circular modes in a vibrating string
| When a simple stretched string is driven sinusoidally using a mechanical vibrator in a plane and made to resonate, non linearities are observed. In this case, the transverse vibrations are not polarized in one plane; and the motion of the string becomes elliptic as the amplitude of the vibration increases. This is called the circular mode of vibration. The approximate solution of the equations of motion shows that the trajectory is an ellipse. The experiment is the continuation of the quest to model this motion efficiently and to gain a deeper understanding of the behavior of the circular modes. A stretched string, fixed at one end to a rigid support and attached to a hanging weight at other end, is made to resonate. A camera, which has been calibrated to measure the width of an object at a fixed distance in front of it, is used to capture the images of the two perpendicular polarizations of the string. The images are processed to calculate the maximum displacement of the string in both of the planes. We use the elliptical path modelling to represent the circular modes. |
Development of a Portable Atomic Force Microscope
| AFM (Atomic Force Microscope) is used in very high resolution microscopy, with typical resolution of 0.16 nanometer. With different operational modes AFM can be used to image almost any type of samples from solid metals to biomedical specimens. The physlab is developing a teaching and basic-research grade AFM in-house. The basic principle lies on cantilever deflection when scanned very close to the sample. A laser beam is used to detect the deflection of cantilever by using photo detector. |  |
High Temperature Precision Dielectric Cell
Measurement of energy band gap in semiconductors
| We are designing an experiment for the fast and reliable measurements of the temperature dependence of electrical conductivity in semiconductor and metallic samples. The energy band gap can be calculated from the data taken in the intrinsic region, and the temperature dependence of the majority carrier mobility can be deduced from measurements taken in extrinsic region. Important parameters are, temperature controlling which is being done by using ‘Multi-Zone Controller’ and resistance measurement using ‘Four Probe Method’. |  |
Low Temperature Heat Capacities and Phase Transitions
| This is a very interesting and simple experiment to determine the low temperature heat capacities using a homemade demonstration of the technique of thermo-gravimetric analysis (TGA). The latent heat of vaporization can then be used to experimentally determine the specific heats of various metals at low temperatures. Spin re-ordering temperature such as the famous Verwey transition in ferrites can also be explored. |  |
Heaters and Refractory Materials
| We have developed disk, cartridge and ring heaters of variable dimensions to fit our requirements in the lab. We make our own thermal cement and raisin. We can also make ceramic sheets (perforated) with different raisins for making shelves and walls of our lab furnaces and micro-ovens.
Currently we can make cartridge heaters ranging from 4 mm in diameter and 20 mm in length to 20 mm in diameter and 300 mm in length. All heaters are made on demand and we also make these for other departments. With additional equipment we can introduce temperature control also. We are also developing `temperature stable' cavities as small as 20 mm in diameter and 50 mm in length for temperatures ranges of -196 Deg C to 500 Deg C. |
 |
Video tracking of Brownian motion
| We used suspension of uniform Polystyrene Microspheres and with the help of microscope objective, CCD camera and computer software we developed image processing programmes to locate the position of microspheres. By incorporating the mean square displacement of suspended particles in the Einstein’s formula we will calculate the Avogadro’s number and the Boltzmann constant. This formula was derived by applying the van’t Hoff law to suspensions, assuming Stoke’s law and describing the Brownian motion as a diffusion process. |  |
Thermal studies on resistively heated wires
| Our [freshman experiment on the measurement of the Curie temperatures] was very popular. Later, we added susceptibility measurements to the experiment, enabling us to look at the temperature dependent susceptibility. Furthermore, we improved and generalized the technique to determine the analytical temperature of any rapidly resistively heated wire, based on geoemetrical and thermophysical data. We developing a dynamical model for the thermocouple's thermal inertia applicable in such rapid heating conditions. |  |
Thermo-elastic tracking of phase transitions
| Many physical substances undergo phase transition when subjected to heat. Chromium also follows that behavior which is associated with the change in its magnetic order. In this experiment we study the phase transition of Chromium by directly measuring the volume change at Neel temperature. Temperature control is achieved thermoelectrically. Several useful thermodynamical quantities associated with the phase transition can be determined, such as the latent heat and entropy change. |  |
X-ray Fluorescence Spectroscopy
| X-ray fluorescence (XRF) is an elemental analysis technique which provides highly accurate determinations for major elements and a broad elemental survey of the sample composition. The phenomenon is widely used for elemental and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials. When high energy photons (x-rays) fall on the target, they displace inner shell electrons from it. Outer shell electrons then fall into the vacancy left by the displaced electron. In doing so, they normally emit light (fluoresce) equivalent to the energy difference between the two states. Since each element has electrons with unique energy levels, the wavelength of light emitted is characteristic of the element and the intensity of light emitted is proportional to the elements concentration. |  |
| The objective of the proposed experiment is to analyze and study the historical coins of the sub-continent that were minted in the region from approximately 200 BC to 1947 AD. For this purpose, a collaboration with the Lahore museum would be beneficial since these museums possess a treasure of coins which were minted and used during different historical periods. The X-ray spectroscopy of the coins can provide a good opportunity to understand the technology, political and economic history of different reigns and empires of the sub-continent. |  |
Competing Modes of Heat Transfer
| A comparison was done between radiation, convection and conduction under conditions of forced and natural convection. We interrogate heat exchange from different geometries such as cones and fins as well. We placed 16 thermocouples attached to the heating cylinder to find out the heat loss gradient as a function of length. |  |
Explorations in nonlinear physics (electrical and electromechanical systems)
| We have developed new experiments in the nonlinear dynamics series, "Observing Chaos in an RL-Diode Circuit" and "The Magnetic Pendulum" that are now included in Experimental Physics Lab II. They beautifully manifest the notion of chaos and the related non-linearities. Bifurcations and chaos in circuit behavior are observed using different tools, e.g. Fourier Spectra, phase portraits and Poincare Sections as well as the dual mode plots on oscilloscope. |  |
Superconducting Quantum Interference Devices
| Superconducting Quantum interference devices (SQUIDs) are sensitive devices that can detect small changes in the magnetic field. They take advantage of two important properties of superconductors, namely the flux quantization and the Josephson effect. Mr. SQUID is a commercially available high temperature superconducting (HTS) DC SQUID. We have used Mr. SQUID to study the novel phenomena of superconductors and have used is as an extremely sensitive magnetometer and nano-voltmeter. |  |
Muon lifetime measurement
| SSE physlab is developing an experiment on muon life time measurement for junior physics lab. We are also developing a low cost-high speed electronics module based on fast complex programmable logic devices (CPLD) which will act as stand alone signal extracting and logic component in the experiment. |
General research and development
|
Circuit boxes: We make our own circuit boxes depending on the demand in the lab. Boxes are made out of plexiglass or aluminium sheet. |