Welcome to my website:
I am currently a Postdoctoral Fellow in Thomas J. Watson Laboratory of Applied Physics at California Institute of Technology in the group of Prof. Harry Atwater. Before moving to Pasadena, I was a Postdoctoral Scholar at the Nanoscale Science and Engineering Center in the group of Prof. Xiang Zhang at the University of California, Berkeley.
My Ph.D. dissertation under the direction of Prof. Marlan O. Scully at Texas A&M University/Princeton University was directed towards quantum coherence and interference effects at the interface of quantum optics, atomic, molecular and optical physics. My graduate studies was supported by Welch Foundation Graduate Fellowship and Herman F. Heep and Minnie Belle Heep Foundation Graduate Fellowship. My undergraduate studies was also in Physics at Indian Institute of Technology Kanpur, (IITK) India.
Recent Research Highlights:
Flying photonic crystal with a defect enables one-way photon trap                                       
We demonstrated that it is possible to localize photons nonreciprocally in a moving photonic lattice made by spatiotemporally modulating the atomic response, where the dispersion acquires a spectral Doppler shift with respect to the probe direction. A static defect placed in such a moving lattice produces a spatial localization of light in the band gap with a shifting frequency that depends on the direction of incident field with respect to the moving lattice. This phenomenon has an impact not only in photonics but also in broader areas such as condensed matter and acoustics, opening the doors for designing new devices such as compact isolators, circulators, nonreciprocal traps, sensors, unidirectional tunable filters, and possibly even a unidirectional laser.

Figure: Schematic of a spatiotemporally modulated photonic crystal with a static defect membrane at the center of the crystal. The right inset schematically shows reflection (R) and the place of localized mode for two different cases: (upper) no time modulation where the localized mode is reciprocal, (middle and lower) spatiotemporal modulation where the position of localized mode depends on the direction of the incident beam. The photonic crystal is formed (see the left inset) from a driven Rb atom-cell (Λ-type three-level system) with a standing wave field with detuning δ between the two components.

  • P. K. Jha, M. Mrejen, J. Kim, C. Wu, Y. Wang, Y. V. Rostovtsev, and X. Zhang, "Coherence-Driven Topological Transition in Quantum Metamaterials", Phys. Rev. Lett. 116, 165502(2016).   
                                                     Atomic Lattice Quantum Metamaterial: 
                                                     We introduced and theoretically demonstrated a quantum metamaterial made of dense neutral atoms loaded into an inherently defect-free artificial crystal of light. Such periodic atomic density grating -an atomic lattice-exhibits an en ex
treme anisotropic response where the signs of the effective principal dielectric constant are different. We demonstrate an all-optical and ultrafast control over the photonic topological transition of the isofrequency from an open to close topology at the same frequency. Our proposal brings together two important contemporary realms of science - cold atoms in optical lattice and metamaterial- and may lead to practically lossless, tunable and topologically reconfigurable quantum metamaterials for single single- or few-photon-level applications.  

Figure: Schematic of the atomic lattice quantum metamaterial. A dense ensemble of ultra cold atoms into the dipole traps of a 1D far-off-resonant, blue detuned optical lattice. The isofrequency surface of such atomic density grating is open (hyperbolic type) rather than closed (spherical/elliptical) for natural materials

  • P. K. Jha*, X. Ni*, C. Wu, Y. Wang, and X. Zhang, "Metasurface-Enabled Remote Quantum Interference", Phys. Rev. Lett. 115, 025501 (2015) [Editors’ Suggestion, Highlighted in Physics as Focus Story].   
                                                                                                                                                                                                                                                                                                                                 Quantum Metasurface: Harnessing metasurface for quantum vacuum engineering.
  • We recently introduced and theoretically demonstrate a strong anisotropic quantum vacuum (AQV) over macroscopic distances enabled by a judiciously designed array of subwavelength-scale nanoantennas -a metasurface. We harness the phase-control ability and the polarization-dependent response of the metasurface to achieve strong anisotropy in the decay rate of a quantum emitter located over distances of hundreds of wavelengths. Such an AQV induces quantum interference among radiative decay channels in an atom with orthogonal transition
    Figure: The metasurface creates a strong  AQV in the vicinity of a quantum emitter at some macroscopic distance d. Decay of an in-plane, linear dipole is anisotropic (solid green curve) with respect to an isotropic quantum vacuum with no physical boundary (dashed red line). Such an AQV induces quantum interference among the radiative decay channels with orthogonal dipole transition.                                                                                                                                                                                                                                                                   
                Focus Story: Metamirror Generates Interference at a Distance by David Lindley 
A proposed metasurface made of tiny gold antennas could act as either a flat mirror or a concave, focusing mirror, depending on the radiation pattern of the source, which could lead to new ways to control quantum systems.                                                            
Figure:  A metasurface consisting of gold nanoantennas separated from a gold slab by a thin, nonconducting layer reflects light from a dipole source with a phase shift that varies with position, as indicated by the colored surface. Color at any location corresponds to the magnitude of phase shift for scattering from the point below. 

  • K. E. Dorfman*, P. K. Jha*, D. V. Voronine, P. Genevet, F. Capasso and M. O. Scully, "Quantum-Coherence-Enhanced Surface Plasmon Amplification by Stimulated Emission of Radiation", Phys. Rev. Lett. 111, 043601(2013).
Quantum Plasmonics: Nanolaser go quantum
We investigate surface plasmon amplification in a silver nanoparticle coupled to an externally driven three-level gain medium and show that quantum coherence significantly enhances the generation of surface plasmons. Surface plasmon amplification by stimulated emission of radiation is achieved in the absence of population inversion on the spasing transition, which reduces the pump requirements. The coherent drive allows us to control the dynamics and holds promise for quantum control of nanoplasmonic devices.

A silver nanosphere surrounded by three-level quantum emitters such as atoms, molecules, rare earth ions, or semiconductor quantum dots placed in the near field of a dipolar plasmon mode. Population of the level 2 decays by exciting the surface plasmons. The physical mechanisms involved in the spasing process are analogous to electromagnetically induced transparency and coherent population trapping.