Kunal Das

1. Patent No. US-12287207-B2 UNITED STATES. Date Issued = 04/29/2025
2. Patent No. US-11243079-B2 UNITED STATES. Date Issued = 02/08/2022

My reasearch has spanned multiple areas of physics over the years. A brief overview is given below for each, along with a couple of representative papers. While I am not actively working on some of these topics at the present, they all continue to influence and guide my current research interests. Specifically, the diversity of topics has been indispensible for my long term research on the foundations of modern physics, not described here, but on which I expect to publish soon.

Starting with my doctoral thesis work on Bose-Einstein-condensate (BEC), I have been interested in the  nonlinear Schrödinger equation (NLSE) which provides the mean-field description of interactions. In recent years, with the help of several students, I have done a comprehensive study of the NLSE  with both open and ring-shaped boundary conditions. We developed a unified description of 1D quantum scattering in the presence of interactions, in terms of a single Jacobi elliptic function with a complex phase. This work hs led to a new way for describing scattering of interacting systems with stationary states. In other work, comprehensive spectrum of stationary states of a NLSE has been determined for a BEC trapped in a ring-shaped lattice, for both positive and negative nonlinearities. I have also been interested in interacting quantum systems that use a full quantum description, such as the Bose-Hubbard model. A recent paper showed novel finite size features in small systems of bosons trapped in just a few lattice sites, which vanish in the thermodynamic limit.

• Jian Jun Liu and Kunal K Das, Finite size effects for interacting bosons on small ring lattices, Journal of Physics B, 59 065301 (2026).
• Allison Brattley and Kunal K. Das, Quantum scattering states in a nonlinear coherent medium, Phys. Rev. A 108, 023314 (2023).

Ultracold atoms have become the go-to simulators for quantum phenomena since it scales up quantum behavior from the scale of elementary particles to conglomerations of millions of atoms, as in a BEC. That allows utilizing quantum effects to push the sensitivity of sensors, particularly since matter waves have much shorter wavelengths than typical lasers. Much of my recent work has been in developing ideas for different simulators and sensors using ultracold atoms.  I have had two US patent awards for a new principle based on localization rather than interferometry, for high-precision sensors for rotation and magnetic field. Some recent papers have put forward mechanisms to simulate spin-orbit and hyperfine structures, to implement the Lipkin-Meshkov-Glick model, and to study nonlinear phase transitions and spin squeezing, all using interacting ultracold atoms in ring traps.

• Kunal K. Das, Significance and Sensor Utility of Phase in Quantum Localization Transition, Phys. Rev. Letters 125, 070401 (2020).
• M. Kolar, T. Opatrný, and Kunal K. Das, Criticality and spin squeezing in the rotational dynamics of a Bose-Einstein condensate on a ring lattice, Phys. Rev. A 92, 043630 (2015).

Coherent Transport Adiabatic Passage (CTAP) is an almost magical quantum effect whereby material entities like atoms and electrons can be transferred from one potential well to a non-adjacent potential well without ever having any significant presence in an intervening well. Although it looks on the surface like 'teleportation', it is actually the spatial analog of the well know effect known as Stimulated Raman Adiabatic Passage (STIRAP). I wrote several papers on this phenomenon in the context of ultracold atoms, mostly with my long term collaborator Tomáš  Opatrný, where we identified optimal transfer conditions, generalized to dual interacting species transport without the two species ever overlapping, and designed an atomtronics version of a transistor operation with neutral atoms carriers instead of electrons and holes.

• Miroslav Gajdacz, Tomáš Opatrný and Kunal K. Das, Transparent, Non-local, Species-selective Transport in an Optical Superlattice Superlattice Containing Two Interacting Atom Species, Phys. Rev. A 83, 033623 (2011).
• Miroslav Gajdacz, Tomáš Opatrný and Kunal K. Das, An atomtronics transistor for quantum gates, Phys. Lett. A 378, 1919-1924 (2014).

My interest in mesoscopic transport started during my post-doc at Penn State. I used the Landauer-Büttiker formalism extensively to model transport in nanowires, which are treated as quasi 1D waveguides with different transverse energies acting as distinct channels, and the current driven by the difference in chemical potential. I wrote several papers on adiabatic quantum pumps, in the context of nanoscale transport, and on characterizing mobility in nanowires. This brought me into the general realm of nano-technology, which has been quite useful over the years.

Later, I realized that the same physical setup could be translated to cold atomic systems and wrote a paper on it, specifically suggesting routes to implementing quantum pumps using atom-chips technology. A version of it was subsequently implemented in experiments in the lab of my collaborator, Seth Aubin who was also a coauthor on that initial proposal. I wrote a few other papers on various types of quantum pumping mechanisms, involving different types of time-varying potentials.

• Kunal K. Das, and Seth Aubin, Quantum Pumping with Ultracold Atoms on Microchips: Fermions versus Bosons, Phys. Rev. Lett. 103, 123007 (2009).
• Kunal K. Das, Sungjun Kim, and Ari  Mizel, Controlled Flow of Spin-Entangled Electrons via Adiabatic Quantum Pumping, Phys. Rev. Lett. 97, 096602 (2006).

I have applied stochastic calculus to study both quantum and classical systems. The underlying principles are universal in the sense that they can be applied to all arenas of study including physics, biology and economics, which have noise or randomness in them. My work has utilized both Langevin and Fokker-Planck approaches.  In the quantum regime, I worked with Girish Agarwal, an authority in the field, on a Langevin analysis of fundamental noise limits in some aspects of Coherent Anti-Stokes Raman spectroscopy. On the classical side, I published on stochastic properties of Photoacoustic Raman spectroscopy, and also on calcium signalling in the context of ion channels in biological cells.

• Kunal K. Das, G. S.  Agarwal, Yu. M. Golubev, and M. O. Scully, A Langevin Analysis of Fundamental Noise Limits in Coherent Anti-Stokes Raman Spectroscopy, Phys. Rev. A 71, 013802 (2005).
• Robert Rovetti, Kunal K. Das, Alan Garfinkel,  and Yohannes Shiferaw, Macroscopic consequences of calcium signaling in microdomains: A first passage time approach, Phys. Rev. E 76, 051920 (2007).

n the process of studying quantum pumps, and general quantum scattering by time-varying potentials, a comparison with classical scattering naturally led to bridging of the two limits via semiclassical theory. This lead to several interesting papers with collaborators Seth Aubin and John Delos at The College of William & Mary, and Kevin Mitchell from UC Merced.  Specifically, the semiclassical theory gave excellent agreement with the structure of the Floquet side-bands intrinsic to scattering by time-dependent potentials.

• T.  Byrd, M. Ivory, A. J. Pyle, S. Aubin, J. Delos, K. Mitchell and Kunal K. Das, Scattering by an oscillating barrier: quantum, classical, and semiclassical comparison, Phys. Rev. A 86 013622 (2012).
• Megan K. Ivory, Tommy A. Byrd, Andrew J. Pyle, Kunal K. Das, Kevin A. Mitchell, Seth Aubin, and John B. Delos, Ballistic atom pumps, Phys. Rev. A 90, 023602 (2014).

I wrote several papers on ultracold atoms in 1D, particularly during my postdoctoral years in the Optical Sciences Center working with Marvin Girardeau, who was a pioneer in this field. In those papers, I explore Bose-Fermi mixtures in 1D, and crossover from 1D to 3D, and interference effects. My experience with 1D systems was later useful for studying mesoscopic transport in nanowires, and ultracold atoms in quasi-1D ring traps.

• Kunal K. Das, Bose-Fermi Mixtures in One Dimension, Phys. Rev. Lett. 90, 170403 (2003).
• Kunal K. Das, M. D.  Girardeau and E. M. Wright, Crossover from one to three dimensions for a gas of hard-core bosons, Phys. Rev. Lett. 89, 110402 (2002).

My doctoral work was on the static and dynamical properties of BEC.  I studied the evolution and damping of BEC, and examined how highly anisotropic BEC's crossover from 3D to 2D and 1D. In recent years, I have been interested in the properties of BEC in configurations with non-trivial topology. Wrapping degenerate ultracold atoms around ring shaped traps can make the non-local quantum effects directly manifest in the macroscopic quantum states. An azimuthal lattice makes the system both more interesting and in some ways simpler by introducing a new length scale. Such coherent systems allow a wide range of quantum mechanical effects to be investigated.

• Kunal Das and Thomas  Bergeman, Trends in Resonance Energy Shifts and Decay Rates for Bose-Condensates in a Harmonic Trap, Phys. Rev. A 64, 013613 (2001).
• Kunal Das, Highly anisotropic Bose-Einstein condensates: crossover to lower dimensions, Phys. Rev. A 66, 053612 (2002).