arXiv subjects

Amit Bhunia

Publications and source records attributed to Amit Bhunia.

9 recordsLinked to original sources

arXiv2026

Voltage-Regulated Photoluminescence Modulation in a 0D-2D Mixed Dimensional Heterostructure

Bias dependent oscillations in excitonic photoluminescence are observed in a mixed dimensional 0D 2D heterostructure. These oscillations arise from modulation by oscillatory DC photocurrent, which exhibits periodic negative differential resistance, indicating recurring charge accumulation within the heterostructure. The persistence of these oscillations across a macroscopic area of diameter around 200 microns suggests the presence of periodically correlated quantum phenomena over large length scales. Furthermore, bias dependent oscillations in the photo capacitance are observed, reflecting a periodic ordering and disordering of excitonic populations. Together, these observations point to a direct competition between coherent and incoherent electron tunnelling processes. The coupled oscillatory behaviour of photoluminescence, photocurrent, and photo capacitance highlights new opportunities for exciton-based quantum optoelectronic devices.

cond-mat.mes-hall↗

arXiv2025

Stabilizing an optical cavity containing a bulk diamond crystal at millikelvin temperatures in a cryogen-free dilution refrigerator

We successfully stabilized a Fabry-Pérot optical cavity incorporating a bulk diamond crystal at millikelvin temperatures in a cryogen-free dilution refrigerator with the pulse-tube cryocooler running. In stark contrast to previous demonstrations where lasers were locked to the cavities, our setup locks the cavity to a laser. Our measurements of cavity length fluctuation suggest that the setup could stabilize a cavity up to a finesse of $1.2\times 10^4$ without the diamond and $5.8 \times10^3$ with the diamond crystal. The finesse with a diamond crystal of approximately 90 is primarily limited by the absorption loss inside the diamond.

quant-ph↗

arXiv2024

Dielectric microwave resonator with large optical apertures for spin-based quantum devices

Towards a spin-based quantum microwave-optical photon transducer, we demonstrate a low-loss dielectric microwave resonator with an internal quality factor of $2.30\times10^4$ while accommodating optical apertures with a diameter of $8\, \mathrm{mm}$. The two seemingly conflicting requirements, high quality factor and large optical apertures, are satisfied thanks to the large dielectric constant of rutile ($\mathrm{TiO_2}$). The quality factor is limited by radiation loss, and we confirmed by numerical simulation that this dielectric resonator can achieve a quality factor exceeding $10^6$ by extending the height of the resonator enclosure. Using this resonator, we performed both continuous-wave (cw) and pulse electron spin resonance (ESR) spectroscopy on 2,2-diphenyl-1-picrylhydrazyl (DPPH) crystalline powder and P1 centers in a diamond crystal in a dilution refrigerator. The cw ESR spectroscopy demonstrated high-cooperativity and strong spin-resonator coupling with the DPPH and P1 centers respectively, while the pulse ESR spectroscopy successfully measured longitudinal and transverse relaxation times.

quant-ph↗

arXiv2023

Site-specific stable deterministic single photon emitters with low Huang-Rhys value in layered hexagonal boron nitride at room temperature

Development of stable room-temperature bright single-photon emitters using atomic defects in hexagonal-boron nitride flakes (h-BN) provides significant promises for quantum technologies. However, an outstanding challenge in h-BN is creating site-specific, stable, high emission rate single photon emitters with very low Huang-Rhys (HR) factor. Here, we discuss the photonic properties of site-specific, isolated, stable quantum emitter that emit single photons with a high emission rate and unprecedented low HR value of 0.6 at room temperature. Scanning confocal image confirms site-specific single photon emitter with a prominent zero-phonon line at ~578 nm with saturation photon counts of 105 counts/second. The second-order intensity-intensity correlation measurement shows an anti-bunching dip of ~0.25 with an emission lifetime of 2.46 ns. Low-energy electron beam irradiation and subsequent annealing are important to achieve stable single photon emitters.

physics.optics↗

arXiv2023

0D-2D Heterostructure for making very Large Quantum Registers using itinerant Bose-Einstein Condensate of Excitons

Presence of coherent resonant tunneling in quantum dot (zero-dimensional) - quantum well (two-dimensional) heterostructure is necessary to explain the collective oscillations of average electrical polarization of excitonic dipoles over a macroscopically large area. This was measured using photo excited capacitance as a function of applied voltage bias. Resonant tunneling in this heterostructure definitely requires momentum space narrowing of charge carriers inside the quantum well and that of associated indirect excitons, which indicates bias dependent itinerant Bose-Einstein condensation of excitons. Observation of periodic variations in negative quantum capacitance points to in-plane coulomb correlations mediated by long range spatial ordering of indirect, dipolar excitons. Enhanced contrast of quantum interference beats of excitonic polarization waves even under white light and observed Rabi oscillations over a macroscopically large area also support the presence of density driven excitonic condensation having long range order. Periodic presence (absence) of splitting of excitonic peaks in photocapacitance spectra even demonstrate collective coupling (decoupling) between energy levels of the quantum well and quantum dots with applied biases, which can potentially be used for quantum gate operations. All these observations point to experimental control of macroscopically large, quantum state of a two-component Bose-Einstein condensate of excitons in this quantum dot - quantum well heterostructure. Therefore, in principle, millions of two-level excitonic qubits can be intertwined to fabricate large quantum registers using such hybrid heterostructure by controlling the local electric fields and also by varying photoexcitation intensities of overlapping light spots.

cond-mat.quant-gas↗

arXiv2020

Phase Coherent Oscillations of Excitonic Photocapacitance and Bose-Einstein Condensation in Quantum Coupled 0D-2D Heterostructure

We report quantum coherent oscillations of photocapacitance of a double-barrier resonant tunneling heterostructure with bias at 10 K. Periodic presence and absence of sharp excitonic transitions in photocapacitance spectra with increasing bias demonstrate strong coupling between InAs quantum dots (0D) and triangular GaAs quantum well (2D). Coherent resonant tunneling in this 0D-2D heterostructure establishes the momentum space narrowing of excitonic Bose-Einstein Condensation. Drastic increase of indirect exciton densities below 70 K reveal that excitonic wave functions anchored with each InAs quantum dots can laterally overlap across wide region around 200 micron to create a macroscopic quantum state of excitonic Bose-Einstein condensate. This itself points out the difficulties encountered in the usual 2D-2D bilayers and coupled quantum well samples used earlier to study excitonic BEC. Finally, we predict how coupled quantum-dots and quantum-well heterostructures can display excitonic Bose-Einstein condensation at even higher temperatures.

cond-mat.quant-gas↗

arXiv2018

Experimental evidences of trions and Fermi edge singularity in single barrier GaAs/AlAs/GaAs heterostructure using photocapacitance spectroscopy

In this paper, we show how photocapacitance spectra can probe two dimensional excitonic complexes and Fermi edge singularity as a function of applied bias around 100 K. In lower density regimes (<1x1011cm^-2), the appearance of two distinct peaks in the spectra are identified as a signature of coexistence of both excitons and positively charged trions. We estimate the binding energy of these trions as ~2.0 meV. In the higher density regimes (>1x10^11 cm^-2), we observe a sharp spectral transition from trions to asymmetric shaped Fermi edge singularity in the photocapacitance spectra around a particular reverse bias. However, these signatures are absent from the photoluminescence spectra measured under identical circumstances. Such dissimilarities clearly point out that different many body physics govern these two spectral measurements. We also argue why such quantum confined dipoles of spatially indirect trions can have thermodynamically finite probability to survive even around 100 K. Finally, our observations demonstrate that photocapacitance technique, which was seldom used to detect trions in the past, can also be useful to detect the traces of these spatially indirect excitonic complexes as well as Fermi edge singularity even at 100 K. This is mainly due to enhanced sensitivity of such dielectric measurements to dipolar changes within such heterojunction.

cond-mat.mes-hall↗

arXiv2018

Experimental evidences of quantum confined 2D indirect excitons in single barrier GaAs/AlAs/GaAs heterostructure using photocapacitance at room temperature

We investigated excitonic absorptions in GaAs/AlAs/GaAs single barrier heterostructure using both photocapacitance and photocurrent spectroscopies at room temperature. Photocapacitance spectra show well defined resonance peak of indirect excitons formed around the Gamma-AlAs barrier. Unlike DC-photocurrent spectra, frequency dependent photocapacitance spectra interestingly red shift, sharpen up and then decrease with increasing tunneling at higher biases. Such dissimilarities clearly point out that different exciton dynamics govern these two spectral measurements. We also argue why such quantum confined dipoles of indirect excitons can have thermodynamically finite probabilities to survive even at room temperature. Finally, our observations demonstrate that photocapacitance technique, which was seldom used to detect excitons in the past, is useful for selective detection and experimental tuning of relatively small numbers (~10^11/cm2) of photo-generated indirect excitons having large effective dipole moments in this type of quasi-two dimensional heterostructures.

cond-mat.mes-hall↗

arXiv2016

Negative activation energy and dielectric signatures of excitons and excitonic Mott transitions in quantum confined laser structures

Mostly, optical spectroscopies are used to investigate the physics of excitons, whereas their electrical evidences are hardly explored. Here, we examined a forward bias activated differential capacitance response of GaInP-AlGaInP based multi-quantum well laser diodes to trace the presence of excitons using electrical measurements. Occurrence of negative activation energy after light emission is understood as thermodynamical signature of steady state excitonic population under intermediate range of carrier injections. Similar corroborative results are also observed in an InGaAs-GaAs quantum dot laser structure grown by molecular beam epitaxy. With increasing biases, the measured differential capacitance response slowly vanishes. This represents gradual Mott transition of an excitonic phase into an electron-hole plasma in a GaInP-AlGaInP laser diode. This is further substantiated by more and more exponentially looking shapes of high energy tails in electroluminescence spectra with increasing forward bias, which originates from a growing non-degenerate population of free electrons and holes. Such an experimental correlation between electrical and optical properties of excitons can be used to advance the next generation excitonic devices.

cond-mat.mes-hall↗