This page lists my research projects. For a summary of my academic course projects, please see my CV.

Publications

  • C.L. Hsueh*, P. Sriram*, T. Wang, C. Thomas, G. Gardner, M. A. Kastner, M. J. Manfra, D. Goldhaber-Gordon. Clean quantum point contacts in an InAs quantum well grown on a lattice-mismatched InP substrate. Phys. Rev. B 105, 195303 (2022) [Phys.Rev.B], [arXiv:2202.05829]

  • C. Duse, P. Sriram, K. Gharavi, J. Baugh, B. Muralidharan. Role of dephasing on the conductance signatures of Majorana zero modes. J. Phys.: Condens. Matter 33 365301 (2021) [J. Phys.: Condens. Matter], [arXiv:2103.08857]

  • P. Sriram, S. S. Kalantre, K. Gharavi, J. Baugh, and B. Muralidharan. Supercurrent Interference in Semiconductor Nanowire Josephson junctions. Phys. Rev. B, Phys. Rev. B 100, 155431, Oct 2019 [Phys.Rev.B], [arXiv:1902.10947]

  • M. Gopalkrishnan, V. Kandula, P. Sriram, A. Deshpande, and B. Muralidharan. Bayesian view of single-qubit clocks, and an energy versus accuracy tradeoff. Phys. Rev. A 96, 032339, Sept 2017 [Phys.Rev.A], [arXiv:1602.00508]

Conference Proceedings

  • P. Sriram, C.L. Hsueh, T. Wang, C. Thomas, G. Gardner, M.A. Kastner, M.J. Manfra and D. Goldhaber-Gordon. Towards tunable quantum criticality in InAs quantum wells: hybrid metal-semiconductor quantum dots for charge Kondo effects. APS March Meeting 2022, Chicago IL. [Abstract]

  • P. Sriram, S.S. Kalantra, K. Gharavi, J. Baugh, and B. Muralidharan. Quantum-Transport in Semicon- ductor Nanowire Josephson Junctions. APS March Meeting 2019, Boston MA [Abstract]

  • M. Gopalkrishnan, V. Kandula, P. Sriram, A. Deshpande, and B. Muralidharan. A Bayesian view of Single-Qubit Clocks, and an Energy versus Accuracy tradeoff, Proceedings of the 2016 IEEE International Symposium on Information Theory, Barcelona, Spain [ISIT2016]

Research

Exotic Kondo effects in InAs based heterostructures, towards quantum simulation of non-Fermi liquid physics

My research is focussed on developing hybrid InAs-based analog quantum simulators for probing novel phase transitions based on charge Kondo effects. Hybrid metal-semiconductor two-dimensional systems are an attractive platform for exploring correlated electron-electron interactions. Flexible nanopatterning allows design of structures to emulate particular Hamiltonians with electrostatically tunable parameters. Frédéric Pierre recently demonstrated a quantum phase transition based on a multichannel charge Kondo effect[1,2] in a GaAs heterostructure with an annealed metal island. InAs may offer significant advantages: pinning of the surface Fermi level in the conduction band allows for direct electrical contact to metals. Small metallic islands with large charging energies may allow building on earlier charge Kondo work without requiring as low electron temperatures. Furthermore, pristine interfaces with epitaxially grown superconducting Aluminum offers new avenues for studying strongly correlated systems[3]. I have been working towards charge Kondo devices on InAs 2DEGs as a quantum simulation platform of non Fermi-liquid phases.

References

  1. Z. Iftikhar, et al., Nature 526, 233–236 (2015)
  2. Z. Iftikhar, et al., Science 360, 1315–1320 (2018)
  3. A. Fornieri, et al., Nature 569, 89–92 (2019)

Previous work

1. Supercurrent Interference in Semiconductor Nanowire Josephson junctions

Under the guidance of Prof. Bhaskaran Muralidharan, and Prof. Jonathan Baugh at IQC Waterloo and IIT Bombay

Presented at the APS March Meeting 2019. Abstract

Semiconductor-superconductor hybrid systems provide a promising platform for hosting unpaired Majorana fermions towards the realisation of fault-tolerant topological quantum computing. In this study, we employ the Keldysh Non-Equilibrium Green’s Function (NEGF) Formalism to model quantum transport in normal-superconductor junctions. We analyse semiconductor nanowire Josephson junctions (InAs/Nb) using a three-dimensional discrete lattice model described by the Bogolubov-deGennes Hamiltonian in the tight-binding approximation, and compute the Andreev bound state spectrum and current-phase relations. We go beyond the Andreev approximation limit and investigate the interesting features observed in the conductance and current spectral density outside this limit. Recent experiments [1] and [2] reveal critical current oscillations in these devices, and our simulations confirm these to be an interference effect of the transverse subbands in the nanowire. We add disorder to model coherent scattering and study its effect on the critical current oscillations, with an aim to gain a thorough understanding of the experiments.

References

  1. K. Gharavi, J. Baugh arXiv:1405.7455v2
  2. Zuo, et. al. Phys. Rev. Lett. 119, 187704 (2017)
  3. K. Gharavi, J. Baugh Phys. Rev. B 91, 245436, 30 June 2015

2. A Bayesian View of Quantum Clocks

Under the guidance of Prof. Manoj Gopalkrishnan and Prof. Bhaskaran Muralidharan at IIT Bombay

Accepted for a talk at Q-Turn 2018, at Florianópolis, Brazil

We bring a Bayesian approach to the analysis of clocks. Using exponential distributions as priors for clocks, we analyze how well one can keep time with a single qubit freely precessing under a magnetic field. We find that, at least with a single qubit, quantum mechanics does not allow exact timekeeping, in contrast to classical mechanics, which does. We find the design of the single-qubit clock that leads to maximum accuracy. Further, we find an energy versus accuracy tradeoff—the energy cost is at least kT times the improvement in accuracy as measured by the entropy reduction in going from the prior distribution to the posterior distribution. We propose a physical realization of the single-qubit clock using charge transport across a capacitively coupled quantum dot.

3. Spin Qubits in Germanium Hutwires, and Superconducting CPW Resonators for cQED

Under the guidance of Prof. Georgios Katsaros at IST Austria

My work involved the SEM imaging and design of contacts on Germanium nanowires grown on monocrystalline Silicon substrates. I worked with low-temperature experiments in characterising the conductance and transfer response of these nanowires in a 4 K Helium setup. I designed Niobium resonators, and performed extensive simulations on Sonnet to extract loaded quality factor and coupling rate, and measured the spectral response of a Nb resonator at 4 K.