Research

Major Recent Contributions:

I) Quantum Electrodynamics

On 14th September 2015, gravitational waves were detected through an optical interferometry technique. Even though these ripples in space-time have been categorically isolated, important questions about gravitational waves remain. One outstanding question is related to how photons (quantum radiation) can be generated and detected by effective gravitational fields (eg: accelerated observers). My research team expects that the detection of such radiation arising from quantum noise will be a stimulating endeavor for the coming decades fueled by technological advances in ultra-high precision low light level measurements. Towards this and related goals, our group has developed theoretical approaches for understanding quantum and thermal noise in light-matter interactions.

Vacuum Fluctuations: We discovered a unique singular resonance in the conversion of vacuum fluctuations (quantum noise) into heat due to bodies in relative motion [1]–[3]. This phenomenon of vacuum friction has not been observed till date and we are currently exploring connections of our effect to quantum light generation in gravitational fields (Unruh-Hawking radiation).

The accompanying figure depicts two parallel metallic plates in relative motion separated by a small fixed gap. Even though the plates are not in contact, vacuum fluctuations causes a frictional drag force slowing the moving plate. We discovered the existence of a unique negative frequency resonance which causes a giant enhancement in this vacuum drag.

[1]        Y. Guo and Z. Jacob, “Singular evanescent wave resonances in moving media,” Opt. Express, vol. 22, no. 21, pp. 26193–26202, Oct. 2014.

[2]        Y. Guo and Z. Jacob, “Giant non-equilibrium vacuum friction: role of singular evanescent wave resonances in moving media,” J. Opt., vol. 16, no. 11, p. 114023, Nov. 2014.

[3]        S. Pendharker, Y. Guo, F. Khosravi, and Z. Jacob, “PT-symmetric spectral singularity and negative-frequency resonance,” Phys. Rev. A, vol. 95, no. 3, p. 33817, 2017.

 

 

Single Photon Physics: Similar to ubiquitous light sources such as the laser – single photon sources of radiation and their detection is of technological relevance for ultra-secure communications and low lightlevel imaging/sensing. My group has recently started work on theoretical modeling of superconducting nanowire single photon detectors to improve their detection efficiency, timing jitter and dark count. In related work, we have theoretically proposed and experimentally demonstrated long-range dipole-dipole interaction (super-Coulombic energy transfer [1]) between dye molecules and quantum dots. These interactions are traditionally limited to only 10 nm so our approach has potential for applications in scaling up of quantum light sources/detectors [2]. The accompanying figure depicts two quantum emitters exhibiting long-range dipole dipole interactions mediated by a 2D material.

[1]   C. L. Cortes and Z. Jacob, “Super-Coulombic atom–atom interactions in hyperbolic media,” Nat. Commun., vol. 8, p. 14144, Jan. 2017

[2]   Limits to single photon transduction by a single atom: Non-Markov theory L.P. Yang, H. X. Tang, Z. Jacob, under review

 

 

II) Spin and Topology

The Physics Nobel Prize in 2016 was awarded for seminal work on topological phases of electronic matter conducted in the early 1980s. It is remarkable that most current work (barring a select few examples) are related to fermions i.e. systems with half-integer spin. On the other hand, bosonic topological phases have not been discovered experimentally and even the theoretical foundations remain elusive. Light is a boson with spin-1 and we have put forth a new theoretical framework [1], [2] which we call the Dirac-Maxwell correspondence principle to understand the topological phases of light. We have discovered the existence of a spin -1 bosonic topological phase for light (paper under review [3]) and also shown for the first time – existence of Photonic Dirac monopoles, Dirac strings, photonic skyrmions, helicity quantization and topological quantum numbers stemming from a parity-time anomaly for photons. The accompanying figure describes the concept of an inherent spin-momentum locking that we predicted in the textbook phenomenon of total internal reflection.

[1]        T. Van Mechelen and Z. Jacob, “Universal spin-momentum locking of evanescent waves,” Optica, vol. 3, no. 2, pp. 118–126, 2016.

[2]        F. Kalhor, T. Thundat, and Z. Jacob, “Universal spin-momentum locked optical forces,” Appl. Phys. Lett., vol. 108, no. 6, p. 61102, Feb. 2016

[3]         T. V. Mechelen and Z. Jacob ” Dirac-Maxwell Correspondence: Spin 1 Bosonic Topological Insulator”, Under Review (arXiv:1708.08192)

 

 

III) Thermal Engineering

Another major application being pursued in my group is related to thermophotovoltaics – conversion of thermal energy into electricity. This derives on theoretical work connecting thermal noise to Maxwell’s equations using techniques pioneered by S.M. Rytov called “fluctuational/stochastic electrodynamics”. In a series of theory papers which culminated into a recent experimental demonstration [1]–[4], we showed the potential of high temperature nanostructures and thermal metamaterials to shape the thermal emission spectrum for waste heat energy harvesting. A related endeavor on thermal noise led us to predict the existence of broadband thermal emission beyond the black body limit in metamaterials/2D materials [5], [6]. In addition, we are pursuing the design of devices such as heat sinks and heat routers for addressing long-standing problems in nanoscale thermal management.

[1]        S. Molesky, C. J. Dewalt, and Z. Jacob, “High temperature epsilon-near-zero and epsilon-near-pole metamaterial emitters for thermophotovoltaics,” Opt. Express, vol. 21, no. S1, pp. A96–A110, Jan. 2013.

[2]      S. Molesky and Z. Jacob, “Ideal near-field thermophotovoltaic cells,” Phys. Rev. B, vol. 91, no. 20, p. 205435, 2015.

[3]      S. Pendharkar, H. Hu, S. Molesky, R. Starko-Bowes, Z. Poursoti, S. Pramanik, N. Nazemifard, R. Fedosejevs, T. Thundat, and Z. Jacob, “Thermal graphene metamaterials and epsilon-near-zero high temperature plasmonics,” J. Opt., accepted early posting online 2017.

[4]      P. N. Dyachenko, S. Molesky, A. Y. Petrov, M. Störmer, T. Krekeler, S. Lang, M. Ritter, Z. Jacob, and M. Eich, “Controlling thermal emission with refractory epsilon-near-zero metamaterials via topological transitions,” Nat. Commun., vol. 7, p. 11809, Jun. 2016

[5]        Y. Guo and Z. Jacob, “Fluctuational electrodynamics of hyperbolic metamaterials,” J. Appl. Phys., vol. 115, no. 23, p. 234306, 2014.

[6]        Y. Guo, C. L. Cortes, S. Molesky, and Z. Jacob, “Broadband super-Planckian thermal emission from hyperbolic metamaterials,” Appl. Phys. Lett., vol. 101, no. 13, pp. 131106-131106–5, Sep. 2012

IV) Imaging and Microscopy

The Chemistry Nobel Prize in 2014 was awarded to advances in fluorescence optical microscopy which beat the diffraction limit. However, the practical engineering problem of super-resolution imaging is far from solved especially in the microwave and THz frequency regimes outside the realm of fluorescence microscopy. Furthermore, current techniques achieve excellent 2D resolution (focal plane super-resolution) but lack the same resolution in 3D (axial super-resolution). We have proposed and demonstrated axial super-resolution using total internal reflection fluorescence (TIRF) microscopy [1], [2].  This approach only utilizes signal processing and optical evanescent wave illumination to advance current commercially available TIRF microscopes (eg: Nikkon, Carl Zeiss). My group has also recently utilized electron energy loss spectroscopy in the transmission electron microscope to map the momentum-energy dispersion of plasmonic excitations in silver far beyond the light line [3]. We believe this is the first step towards the challenge of isolating phenomena such as Cherenkov radiation and spatial dispersion (Landau damping) in nanostructures through electron microscopy.

[1]       S. Pendharker, S. Shende, W. Newman, S. Ogg, N. Nazemifard, and Z. Jacob, “Axial super-resolution evanescent wave tomography,” Opt. Lett., vol. 41, no. 23, pp. 5499–5502, Dec. 2016.

[2]      S. S. Shende, S. Pendharker, Z. Jacob, and N. Nazemifard, “Total Internal Reflection Fluorescence Microscopy To Investigate the Distribution of Residual Bitumen in Oil Sands Tailings,” Energy Fuels, vol. 30, no. 7, pp. 5537–5546, Jul. 2016.

[3]      P. Shekhar, M. Malac, V. Gaind, N. Dalili, A. Meldrum, and Z. Jacob, “Momentum-Resolved Electron Energy Loss Spectroscopy for Mapping the Photonic Density of States,” ACS Photonics, vol. 4, no. 4, pp. 1009–1014, Apr. 2017.

 

V) Fabrication/Devices

Over the years, my research group has also developed a suite of nanofabrication approaches (eg: 10 nm thin films with nm scale smoothness, large area 30 nm diameter nanowire arrays, electron beam and helium ion lithography of nanoantennas etc.) to build photonic devices. Some initial achievements include demonstration of Ferrel-Berreman modes in epsilon-near-zero plasmonic media [1] and gold nanowire based epsilon-near-pole media [2]. One major achievement is related to light confinement for on-chip nanophotonic devices [3]–[6]. The phenomenon of total internal reflection (TIR) of light lies at the heart of light guiding by optical fibers but it also places stringent restrictions on the minimum size of photonic devices achievable on-chip. Using all-dielectric metamaterials, we have controlled this fundamental phenomenon of TIR and demonstrated optical waveguides for dense photonic integrated circuits in silicon chips.

[1]       W. D. Newman, C. L. Cortes, J. Atkinson, S. Pramanik, R. G. DeCorby, and Z. Jacob, “Ferrell–Berreman Modes in Plasmonic Epsilon-near-Zero Media,” ACS Photonics, vol. 2, no. 1, pp. 2–7, 2014.

[2]      R. Starko-Bowes, J. Atkinson, W. Newman, H. Hu, T. Kallos, G. Palikaras, R. Fedosejevs, S. Pramanik, and Z. Jacob, “Optical characterization of epsilon-near-zero, epsilon-near-pole, and hyperbolic response in nanowire metamaterials,” JOSA B, vol. 32, no. 10, pp. 2074–2080, 2015.

[3]      S. Jahani and Z. Jacob, “Transparent subdiffraction optics: nanoscale light confinement without metal,” Optica, vol. 1, no. 2, p. 96, Aug. 2014.

[4]      S. Jahani and Z. Jacob, “Photonic skin-depth engineering,” J. Opt. Soc. Am. B, vol. 32, no. 7, pp. 1346–1353, Jul. 2015.

[5]      S. Jahani and Z. Jacob, “Breakthroughs in Photonics 2014: Relaxed Total Internal Reflection.”IEEE Photonics Journal, 7, 3, 2015

[6]      S. Jahani and Z. Jacob, “All-dielectric metamaterials,” Nat. Nanotechnol., vol. 11, no. 1, pp. 23–36, 2016.