Rajat Theoretical physics

ISF Postdoctoral Fellow · Ben-Gurion University

How quantum matter
finds order.

I am a theoretical physicist studying how collective behaviour emerges in ultracold quantum gases and correlated bosonic systems. My work connects supersolidity, nonequilibrium dynamics, collective excitations and quantum chaos with observables that experiments can measure.

I currently work with Prof. Doron Cohen at Ben-Gurion University of the Negev, combining analytical many-body theory, semiclassical methods and large-scale numerical calculations.

Download CV Google Scholar ORCID
8
published papers
4
first-author
1
accepted paper
52
citations
5
h-index

Publication record and Google Scholar metrics updated 21 August 2026.

Latest

Research updates

Paper on spin and density excitations of one-dimensional self-bound Bose–Bose droplets accepted in Physical Review A.

Accepted article

Published spectrum tomography of metastability and quantum chaos in Bose–Hubbard rings and chains.

Phys. Rev. Research

Published the finite-temperature phase diagram and collective modes of coherently coupled Bose mixtures.

Phys. Rev. A 113, 043310

European Commission Seal of Excellence for the MSCA-PF proposal SuperSQF, evaluated at 92.6/100.

Research profile

Collective behaviour
in quantum gases.

My research examines how interactions, temperature and confinement shape the phases and dynamics of ultracold bosons. I connect microscopic many-body models to experimentally accessible quantities such as collective-mode frequencies, phase boundaries, correlation functions and many-body spectra.

The calculations combine Bogoliubov theory, finite-temperature Hartree–Fock–Bogoliubov methods, real-time Gross–Pitaevskii dynamics, phase-space analysis and exact diagonalisation. The themes below are grounded in published work.

01

Phases and spectroscopy

Supersolids and coherently coupled condensates

I use excitation spectra to identify broken symmetries and phase transitions in spin–orbit-coupled spinor gases, stripe supersolids and Rabi-coupled Bose mixtures.

02

Far from equilibrium

Quenches, domains and universal scaling

Real-time simulations follow the formation and growth of magnetic domains after a quench, connecting microscopic dynamics to correlation-function collapse and a measured coarsening exponent.

03

Correlated bosons

Metastability and quantum chaos

For Bose–Hubbard rings and chains, I combine classical phase-space structure with many-body spectra to diagnose stability, chaos, self-trapping and persistent currents.

Selected contributions

From collective modes to nonequilibrium scaling

My work builds a continuous methodological path from spectra and finite-temperature phase boundaries to domains, coarsening and correlated many-body dynamics.

Nonequilibrium dynamics2025

Dynamic scaling in a spinor quantum gas

Magnetic domains after a zero-momentum-to-plane-wave quench in a homogeneous quasi-2D spin-1 condensate grow as L(t) ∝ t0.66, consistent with inertial-hydrodynamic binary-fluid coarsening. The ensemble and correlation-function workflow is the direct methodological precursor of my supersolid programme.

Phys. Rev. A 111, 033316
Finite temperature2024–25

Thermal control and melting of stripe order

Finite-temperature HFB–Popov calculations show that temperature can shift the plane-wave–stripe boundary and induce stripe order in a trapped quasi-1D gas, while the homogeneous system displays thermal melting and phase-boundary shifts.

PRA 109, 033319 NJP 27, 043005
Spectroscopy2022–26

Collective modes as phase diagnostics

Bogoliubov and variational calculations identify density, spin, Goldstone and roton-like responses across Raman- and angular-momentum-coupled condensates, turning changes of symmetry into experimentally accessible spectra.

PRA 106, 013304 PRA 111, 023311
Correlated bosons2026

Metastability and spectrum tomography

Many-body exact diagonalisation and semiclassical phase-space analysis connect metastable currents with mixed regular–chaotic dynamics in Bose–Hubbard rings and chains.

Phys. Rev. Research 8, 033024

Research in figures

Published results,
seen directly.

Selected calculations from my papers, organised around three questions: how collective modes reveal phase transitions, how temperature reshapes ordered phases, and how classical phase-space structure appears in a quantum spectrum.

Collective modes and coarsening · 2025

From a soft mode to universal domain growth

Phys. Rev. A 111, 033316
Low-lying collective-mode frequencies of a trapped spin-1 sodium condensate versus Raman coupling, showing characteristic minima and softening at phase boundaries
Fig. 4 — collective-mode spectrum. Spin-dipole and spin-breathing modes reach minima near the stripe-to-plane-wave boundary, while the density-dipole mode softens at the plane-wave-to-zero-momentum boundary.
Longitudinal-magnetisation domains at three progressively later times after a zero-momentum-to-plane-wave quench
Fig. 8(c) — real-space coarsening. After the quench, small magnetic domains disappear and a growing characteristic length emerges.
Correlation functions at different times and their collapse when distance is rescaled by the characteristic domain length
Fig. 9(a) — scaling collapse. Correlations measured at different times collapse onto a common curve when distance is expressed in units of the domain scale L(t).
Characteristic coarsening length versus time with a power-law fit proportional to time to the power 0.66
Fig. 9(b) — growth law. The characteristic length follows L(t) ∝ t0.66, consistent with inertial-hydrodynamic binary-fluid coarsening.

Experimental connection. Figure 4 concerns a trapped spin-1 condensate. In a closely related two-component 41K Raman-coupled supersolid, the ICFO group led by Prof. Leticia Tarruell has since observed a stripe-compression mode and its frequency softening at the supersolid transition in Science 391, 480–484 (2026) .

Finite-temperature quantum gases · 2024–25

Temperature can amplify or melt stripe order

PRA 109, 033319 NJP 27, 043005
Zero- and finite-temperature density profiles with a temperature-versus-Raman-coupling phase diagram for a trapped spin-orbit-coupled Bose gas
PRA Fig. 1 — thermal induction. For the trapped parameters studied, a zero-temperature plane-wave state develops a stripe-modulated density at finite temperature.
Finite-temperature phase diagram of a homogeneous spin-1 spin-orbit-coupled Bose gas, with stripe, plane-wave and zero-momentum regions
NJP Fig. 3 — thermal melting. The homogeneous spin-1 phase diagram shows the stripe region shrinking with temperature and the boundaries between stripe, plane-wave and zero-momentum phases.
Metastability and quantum chaos · 2026

Reading phase space through a many-body spectrum

Phys. Rev. Research 8, 033024
Exact Bogoliubov frequencies versus interaction strength for a 51-site Bose-Hubbard chain, with complex-frequency regions marked in magenta
Fig. 3(b) — finite-chain stability. For a 51-site chain, the exact Bogoliubov calculation pushes the onset of complex frequencies to large interaction strength; that unstable regime is excluded in the Gross–Pitaevskii limit.
Fig. 10 · first rowFive-site ring: energetically stable stationary point
u = 4, φ = 1.1π
Energy landscapeClassical occupation-energy landscape for a five-site Bose-Hubbard ring
Classical spectrumLong-time classical occupation-energy spectrum for the same five-site ring
Quantum spectrumMany-body quantum occupation-energy spectrum for the same five-site ring with 30 particles
Fig. 12 · completeFive-site chain across three interaction regimes
Quantum panels: N = 30, odd-parity states excluded
u = 0.5quasi-regular; stable stationary point
Five-site chain energy landscape at interaction strength 0.5 Five-site chain classical spectrum at interaction strength 0.5 Five-site chain quantum spectrum at interaction strength 0.5
u = 3.5chaotic; unstable stationary point
Five-site chain energy landscape at interaction strength 3.5 Five-site chain classical spectrum at interaction strength 3.5 Five-site chain quantum spectrum at interaction strength 3.5
u = 7.5separated chaotic sea and stability island
Five-site chain energy landscape at interaction strength 7.5 Five-site chain classical spectrum at interaction strength 7.5 Five-site chain quantum spectrum at interaction strength 7.5

Across the columns, a phase-space landscape is converted into a long-time classical spectrum and compared with the corresponding many-body quantum spectrum. Increasing interaction reveals chaos, self-trapping and the limits of quantum resolution of small classical stability islands.

Figure sources and reuse information

Every panel is linked to its paper above. Figures from the 2024 and 2025 author manuscripts are available under CC BY 4.0; the 2026 spectrum-tomography panels are reproduced from the authors’ manuscript. Only resizing and PDF-to-image conversion were applied. Explanatory captions on this page are shortened from the original paper captions.

Publications

Peer-reviewed research

Peer-reviewed articles and accepted work, listed newest first.

Complete Scholar profile
Showing 9 of 9
  1. 2026Accepted · Phys. Rev. A

    Spin and density excitations of one-dimensional self-bound Bose–Bose droplets

    Ritu, Rajat, Manpreet Singh, Rajesh Kumar Gupta and Sandeep Gautam

    DOIarXiv
  2. 2026Phys. Rev. Research 8, 033024

    Metastability, chaos, and spectrum tomography for Bose–Hubbard rings and chains

    Rajat and Doron Cohen

    DOIarXiv
  3. 2026Phys. Rev. A 113, 043310

    Finite-temperature phase diagram and collective modes of coherently coupled Bose mixtures

    Sunilkumar V, Rajat, Sandeep Gautam and Arko Roy

    DOIarXiv
  4. 2025New J. Phys. 27, 043005

    Thermal amplification and melting of phases in spin-orbit-coupled spin-1 Bose–Einstein condensates

    Ritu, Rajat, Arko Roy and Sandeep Gautam

    DOIarXiv
  5. 2025Phys. Rev. A 111, 033316

    Collective excitations and universal coarsening dynamics of a spin-orbit-coupled spin-1 Bose–Einstein condensate

    Rajat, Paramjeet Banger and Sandeep Gautam

    DOIarXiv
  6. 2025Phys. Rev. A 111, 023311

    Excitations of a supersolid annular stripe phase in a spin-orbital-angular-momentum-coupled spin-1 Bose–Einstein condensate

    Paramjeet Banger, Rajat and Sandeep Gautam

    DOIarXiv
  7. 2024Phys. Rev. A 109, 033319

    Temperature-induced supersolidity in spin-orbit-coupled Bose gases

    Rajat, Ritu, Arko Roy and Sandeep Gautam

    DOIarXiv
  8. 2023Phys. Rev. A 108, 043310

    Quantum phases and the spectrum of collective modes in a spin-1 Bose–Einstein condensate with spin-orbital-angular-momentum coupling

    Paramjeet Banger, Rajat, Arko Roy and Sandeep Gautam

    DOIarXiv
  9. 2022Phys. Rev. A 106, 013304

    Collective excitations in cigar-shaped spin-orbit-coupled spin-1 Bose–Einstein condensates

    Rajat, Arko Roy and Sandeep Gautam

    DOIarXiv

Academic path

Methods built around physical questions

My trajectory moves from collective excitations, through finite-temperature phase structure and coarsening, to current work on many-body metastability. It provides the analytical and numerical base for an independent programme on coupled-order dynamics.

Bogoliubov theoryCollective modes, stability and roton softening
Real-time GPEQuench ensembles, correlations, domains and defects
HFB–Popov theoryFinite-temperature phase diagrams and spectra
Exact diagonalisationQuantum spectra, metastability and phase-space tomography
Scientific computingFortran, Python, Mathematica, OpenMP/OpenACC and Slurm

ISF Postdoctoral Fellow

Ben-Gurion University of the Negev, Israel

Metastability, quantum chaos and phase transitions in Bose–Hubbard rings and chains, with Prof. Doron Cohen.

Visiting Researcher

Indian Institute of Technology Ropar, India

Collective excitations and finite-temperature dynamics in coupled ultracold gases.

Senior Research Fellow

Indian Institute of Technology Ropar, India

Doctoral research on spin-orbit-coupled spinor condensates and numerical many-body methods.

PhD in Physics

Indian Institute of Technology Ropar, India

Collective excitations and coarsening dynamics of spin-orbit-coupled spinor condensates. Degree awarded 16 July 2025.

Junior Research Fellow

Indian Institute of Technology Ropar, India

Recognition & communication

Research made visible

I communicate results across ultracold-atom, atomtronics and quantum-materials communities, and I have contributed to teaching and mentoring in numerical quantum physics.

2026

European Commission Seal of Excellence

MSCA-PF proposal SuperSQF – Supersolidity in Quantum Fluids, 92.6/100.

2026

Atomtronics, Benasque

Poster on metastability, chaos and spectrum tomography in Bose–Hubbard rings and chains.

2025

Best Oral Presentation, PHYCON

Talk on collective excitations and universal coarsening dynamics in a spin-orbit-coupled spin-1 condensate.

2024

Ultracold Atoms Japan, OIST

Poster on temperature-induced supersolidity in spin-orbit-coupled Bose gases.