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Current Research Ideas!
What makes something quantum and where lies the quantumness?
A superposition of charge and phonon!
Research work done during first postdoc in Quantronics group...
Andreev bound states in InAs nanowire superconducting weak links
Bound states are formed when quantum particles are confined by barriers. When a non-superconducting material is sandwiched between two superconducting leads, localised Andreev bound states (ABSs) form within the non-superconducting channel.
We realize ABSs in Indium Arsenide (InAs) nanowire sandwiched between Aluminum (Al) leads. Due to the strong spin orbit coupling in InAs the ABSs come with a spin texture, which makes this hybrid even more interesting.
Microwave spectroscopy and Andreev Qubits
Microwave spectroscopy is a non-invasive tool to probe ABSs spectra, which usually requires the ABSs to be mapped to the resonance frequency of a microwave resonator. ABSs, being the state bound by superconucting leads, have the natural tendency to nicely couple with superconducting circuits, making these the basis states for potential qubits. The high frequency operation of qubits, in turn, makes microwave spectroscopy a very useful tool to charectirize ABSs.
Currently we are working on Andreev pair qubit, the simplest possible qubit which involve zero quasiparticle ground state and the two quasiparticle excited state, in presence of poisoning. Another goal of our experiment is to exploit the spin texture of ABSs to realize spin qubits.
Research work done during PhD...
Andreev reflection in graphene - superconductor junction
Andreev reflection is the process in which an electron from a normal metal transmits into a superconductor by reflecting back a hole.
Graphene, a single layer of graphite, has a Dirac like dispersion. As a consequence graphene - superconductor junction makes a interesting system where one can observe interplay of relativistic dynamics and superconductivity.
Andreev reflection in quantum Hall regime
Quantum Hall effect is one of the greatest discovery of 20th century after the discovery of superconductivity. Its junction with superconductor provides a very interesting platform to realize topological excitations such as Majorana fermions. Fractional quantum Hall effect is even more interesting, and its junction with superconductor can host exotic non abelian states.
Shot noise measurements and Johnson noise thermometry
Shot noise is a specific type of fluctuation of current that arises due to the discrete nature of underlying current carrying particles. The definition itself says the importance of shot noise, it can be used to measure the quantum of particle responsible for the flow of corresponding current. The schematic to right shows a shot noise measurement setup to measure the quasiparticle charge in the fractional quantum Hall states in 2DEG (two dimensional electron gas).
Johnson noise or thermal noise is the random fluctuation in a resistive component of voltage due to thermal agitation. Being a parameter directly related to temperature of a system, it is very useful for thermometry. In one of our recent work we employed Johnson noise thermometry to show the universality of thermal conductance in integer and fractional quantum Hall effect in graphene.
Coulumb drag measurement
Coulomb drag is an unique tool to observe coulomb interaction in mesoscopic systems. Due to Its non-invasive nature it captures minute correlations those are impossible to realize by conventional conductance measurements. Our specific interest is in understanding the effect of dimensionality on the Coulomb interaction among different low dimensional systems.
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