Hi, I'm

Sushanth Varada,

a first-year Physics PhD student, advised in Quantum Matter Theory by Prof. Annica Black-Schaffer at Uppsala University, Sweden. 

My research focuses on topological states of matter, strongly correlated electron systems, and superconductivity. 

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Email: sushantvarada@gmail.com   

News

Archived News

Publications

Research Papers

2020

S. Varada, S. Katpally, S.S.L. Thiruveedhi, Springer J. Electron. Test. 36, 343-363 (2020)

Theses

Chalmers University of Technology, Supervisors: Christian Spånslätt, Matteo Acciai, Janine Splettstößer

KU Leuven and IMEC, Co-Supervisors: George Simion, Kristiaan De Greve

Select Talks

Research Posters

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.

Visualization of the superconducting phase crystal on the [110] cuprate surface through color-scale plotting of the d-wave order parameter Sin(θ) phase. Image adapted from Chakraborty, Löfwander, Fogelström, and Black-Schaffer, npj Quantum Mater. 7, 44 (2022)

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.

Education

Uppsala University

 PhD Candidate in Physics (Quantum Matter Theory) 

Advisor: Annica Black-Schaffer

Uppsala, Sweden

Expected 2028

Chalmers University of Technology

 Erasmus Mundus Joint MSc. in Nanoscience and Nanotechnology 

Specialization: Quantum Science and Technology

Graduated Magna Cum Laude 

Thesis: Anyon Colliders; Advisor: Janine Splettstößer

Gothenburg, Sweden

2022 - 2023

KU Leuven

 Erasmus Mundus Joint MSc. in Nanoscience and Nanotechnology 

Graduated Magna Cum Laude 

Awards and Activities:

Leuven, Belgium

2021 - 2023

Experience

Interuniversity Microelectronics Centre [IMEC]

 Research Intern 

Supervisor: Alexander Grill

Numerical modeling, cryogenic measurement setup calibration

Leuven, Belgium

7/2022 - 8/2022

Link

Deloitte US-India

 Advisory Associate Solution Advisor 

Information technology audit

Hyderabad, India

6/2019 - 7/2021

Contact

Email: sushantvarada@gmail.com

Postal Address

Department of Physics and Astronomy, 

Division of Materials Theory, 

Uppsala University, Box 516, 

SE-751 20 Uppsala SWEDEN 

Visiting Address

Ångström Laboratory, House 9, Floor 3, Room 93128,

Lägerhyddsvägen 1, Uppsala University 

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