Research

Superconducting Phase Crystal 

Zero-energy flat bands and Density of State (DOS) peaks in the normal state lead to unconventional superconductivity, as seen in materials like stacked graphene layers. What happens to these bands and peaks arising in a superconducting state? They exhibit inherent energetic instability, as observed in [110] surface of d-wave superconductors, where zero-energy flat bands and DOS peaks exist within the surface projection enclosed by bulk nodal points. This likely results in the spontaneous formation of a superconducting phase crystal at the surface.

A phase crystal is a rare state of matter that breaks both time-reversal and translation symmetry through spontaneous nanoscale modulations of the superconducting phase. These phase modulations generate spontaneous supercurrents, magnetic fields, and locally negative superfluid weight, enhancing superconducting properties. This project explores how zero-energy flat bands and DOS peaks may potentially form superconducting phase crystal in different superconductors, drawing insights from high-temperature cuprate superconductor surfaces.

Laughlin Anyons and Fractional Statistics

Quasiparticles arising in 2 space + 1 time dimensions, which obey quantum statistics intermediate between bosons and fermions, are called anyons. The Hong-Ou-Mandel effect reveals fermion and boson exchange statistics through the interference of identical particles at a beam splitter. It was unclear if this interferometry could analyze the anyon exchange statistics by probing their braiding phase. We investigated this question in a Laughlin fractional quantum Hall setup with filling factor 1/(2n+1), where n is a positive integer. Within this setup, we analyze the interference of two anyons at a quantum point contact functioning as a beam splitter for quasiparticles. 

We showed that the standard Hong-Ou-Mandel ratio contains no information about the exchange phase acquired by anyons. Instead, the ratio probes properties related to the scaling dimension of quasiparticle excitations at the quantum point contact. In addition, we developed a physical interpretation of time domain braiding between anyons and quasiparticle excitations to explain erasure of exchange phase effects. 

Optimizing Viterbi Decoder Circuits

The Viterbi algorithm detects symbol sequences modeled as a Markov chain amidst intersymbol interference and noise. Viterbi decoders use this algorithm to navigate a trellis diagram (weighted graph), computing path metrics to reconstruct the original state sequence from a coded, noisy symbol sequence. The Path Metric Unit, with Compare-Select-Add (CSA) and Pre-compute CSA (PCSA) circuits, performs this recursive operation, acting as a crucial power dissipator and potential speed bottleneck in achieving high-throughput Viterbi decoders.

This work attempted bit-level optimization of PMU by replacing the subtractor in CSA and PCSA circuits with an optimized comparator, achieving low latency, low power dissipation, and high reliability. Additionally, single-bit parity signatures were incorporated into the decoders to mitigate memory-based faults. The optimized circuits were designed in Conventional CMOS, Gate Diffusion Input, and Hybrid logic styles using GPDK 90 nm technology library. Simulations were conducted at 27°C with a 1.2V supply rail. We compare simulation results with traditional circuits to emphasize the merits and drawbacks of each design technique.

• Comprehensive Analysis and Optimization of Reliable Viterbi Decoder Circuits Implemented in Modular VLSI Design Logic Styles, S. Varada, S. Katpally, S.S.L. Thiruveedhi, Springer J. Electron. Test. 36, 343-363 (2020)

Interuniversity Microelectronics Centre [IMEC]

 Research Intern 

Supervisor: Alexander Grill

Numerical modeling, cryogenic measurement setup calibration

Deloitte US-India

 Advisory Associate Solution Advisor 

Information technology audit