2026
Srivatsa Murali; Anshuman Kumar
PhoQuPy: A Python framework for Automation of Quantum Optics experiments Journal Article
In: arXiv preprint, vol. arXiv:2602.04505, 2026.
@article{arXiv:2602.04505,
title = {PhoQuPy: A Python framework for Automation of Quantum Optics experiments},
author = {Srivatsa Murali and Anshuman Kumar},
url = {https://doi.org/10.48550/arXiv.2602.04505},
doi = {https://doi.org/10.48550/arXiv.2602.04505},
year = {2026},
date = {2026-02-04},
journal = {arXiv preprint},
volume = {arXiv:2602.04505},
abstract = {We present the automation of a confocal photoluminescence (PL) scanning system for the identification and characterization of single-photon emitters (SPEs) in quantum materials. The setup excites the sample with a laser and acquires a spectrum at each spatial coordinate in a raster scan pattern. A double-acquisition method is used to remove cosmic ray artifacts by comparing subsequent measurements at the same spatial coordinate. Once identified, the emitter is further characterized via a HBT setup, thereby measuring lifetime as well as second-order autocorrelation g(2) measurements to confirm singlephoton emission. The system integrates Python-based hardware control for motorized stages, spectrometer acquisition, and post-processing, with a migration to a galvo-mirror scanning approach for using it along with a cryostat for low temperature measurements. Our results demonstrate spatially resolved PL maps and temperature-dependent spectra, highlighting the capability of the setup to efficiently benchmark SPE performance. We further went on to perform automation of other experiments such as a Non-Linear Interferometry setup for Quantum Imaging with Undetected Light and a Fourier Transform Imaging Spectroscopy using a common path birefringence Interferometer to obtain hyperspectral images of our samples.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present the automation of a confocal photoluminescence (PL) scanning system for the identification and characterization of single-photon emitters (SPEs) in quantum materials. The setup excites the sample with a laser and acquires a spectrum at each spatial coordinate in a raster scan pattern. A double-acquisition method is used to remove cosmic ray artifacts by comparing subsequent measurements at the same spatial coordinate. Once identified, the emitter is further characterized via a HBT setup, thereby measuring lifetime as well as second-order autocorrelation g(2) measurements to confirm singlephoton emission. The system integrates Python-based hardware control for motorized stages, spectrometer acquisition, and post-processing, with a migration to a galvo-mirror scanning approach for using it along with a cryostat for low temperature measurements. Our results demonstrate spatially resolved PL maps and temperature-dependent spectra, highlighting the capability of the setup to efficiently benchmark SPE performance. We further went on to perform automation of other experiments such as a Non-Linear Interferometry setup for Quantum Imaging with Undetected Light and a Fourier Transform Imaging Spectroscopy using a common path birefringence Interferometer to obtain hyperspectral images of our samples.
2025
Anuj Kumar Singh, Parul Sharma, Kishor Kumar Mandal, Lekshmi Eswaramoorthy, Anshuman Kumar
From Atomic Defects to Integrated Photonics: A Perspective on Solid-State Quantum Light Sources Journal Article
In: arXiv preprint, vol. arXiv:2512.14402, 2025.
@article{arXiv:2512.14402,
title = {From Atomic Defects to Integrated Photonics: A Perspective on Solid-State Quantum Light Sources},
author = {Anuj Kumar Singh, Parul Sharma, Kishor Kumar Mandal, Lekshmi Eswaramoorthy, Anshuman Kumar},
url = {https://doi.org/10.48550/arXiv.2512.14402},
doi = {https://doi.org/10.48550/arXiv.2512.14402},
year = {2025},
date = {2025-12-16},
journal = {arXiv preprint},
volume = {arXiv:2512.14402},
abstract = {Single-photon emitters (SPEs) constitute a foundational resource for quantum technologies, including secure communication, photonic quantum computing, and emerging quantum network architectures. A wide range of quantum materials, from atom-like point defects in bulk crystals to excitonic states in low-dimensional semiconductors, now provide bright, coherent, and scalable sources of non-classical light. Meanwhile, advances in photonic integration have enabled efficient routing, filtering, and on-chip manipulation of these emitters. From this perspective, we survey and discuss the technological landscape in which solid-state emitters interface with quantum sensing, quantum communication, quantum computation, and emerging photonic AI platforms. Further, we discuss the materials landscape underpinning modern single-photon sources from the zero-dimensional, one-dimensional, two-dimensional and three-dimensional materials. Lastly, we highlight key integration pathways for these single-photon emitters into scalable quantum photonic systems.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Single-photon emitters (SPEs) constitute a foundational resource for quantum technologies, including secure communication, photonic quantum computing, and emerging quantum network architectures. A wide range of quantum materials, from atom-like point defects in bulk crystals to excitonic states in low-dimensional semiconductors, now provide bright, coherent, and scalable sources of non-classical light. Meanwhile, advances in photonic integration have enabled efficient routing, filtering, and on-chip manipulation of these emitters. From this perspective, we survey and discuss the technological landscape in which solid-state emitters interface with quantum sensing, quantum communication, quantum computation, and emerging photonic AI platforms. Further, we discuss the materials landscape underpinning modern single-photon sources from the zero-dimensional, one-dimensional, two-dimensional and three-dimensional materials. Lastly, we highlight key integration pathways for these single-photon emitters into scalable quantum photonic systems.
Anuj Kumar Singh, Utkarsh Utkarsh, Pablo Tieben, Kishor Kumar Mandal, Brijesh Kumar, Rishabh Vij, Amrita Majumder, Ikshvaku Shyam, Shagun Kumar, Kenji Watanabe, Takashi Taniguchi, Venu Gopal Achanta, Andreas W Schell, Anshuman Kumar
Plasmonic‐Strain Engineering of Quantum Emitters in Hexagonal Boron Nitride Journal Article
In: Advanced Materials Interfaces, pp. 2500071, 2025.
@article{arXiv:2401.11428,
title = {Plasmonic‐Strain Engineering of Quantum Emitters in Hexagonal Boron Nitride},
author = {Anuj Kumar Singh, Utkarsh Utkarsh, Pablo Tieben, Kishor Kumar Mandal, Brijesh Kumar, Rishabh Vij, Amrita Majumder, Ikshvaku Shyam, Shagun Kumar, Kenji Watanabe, Takashi Taniguchi, Venu Gopal Achanta, Andreas W Schell, Anshuman Kumar},
url = {https://doi.org/10.1002/admi.202500071},
doi = {10.1002/admi.202500071},
year = {2025},
date = {2025-06-05},
journal = {Advanced Materials Interfaces},
pages = {2500071},
abstract = {In the realm of quantum information and sensing, there has been substantial interest in the single-photon emission (SPE) associated with defects in hexagonal boron nitride (hBN). With the goal of producing deterministic emission centers, in this work, a platform is presented for engineering emission in hBN integrated with gold (Au) truncated nanocone structures. These findings highlight that, the emission in the hBN overlaps with the emission due to the truncated gold nanocones. Furthermore, the quantum characteristics of this emission are measured and found that while this system demonstrates support for SPE, the origin of this emission remains ambiguous. Specifically, it is unclear whether the emission arises from defects generated by the induced strain or from alternative defect mechanisms. This uncertainty stems from the fluorescence properties inherent to gold, complicating the definitive attribution of the quantum emission source. To provide a rigorous theoretical foundation, the effects of strain are elucidated via the Kirchhoff–Love theory. Additionally, the enhancements observed due to plasmonic effects are comprehensively explained through the resolution of Maxwell's equations. This study will be useful for the development of deterministic and tunable single photonic sources in 2D materials and their integration with plasmonic platforms.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In the realm of quantum information and sensing, there has been substantial interest in the single-photon emission (SPE) associated with defects in hexagonal boron nitride (hBN). With the goal of producing deterministic emission centers, in this work, a platform is presented for engineering emission in hBN integrated with gold (Au) truncated nanocone structures. These findings highlight that, the emission in the hBN overlaps with the emission due to the truncated gold nanocones. Furthermore, the quantum characteristics of this emission are measured and found that while this system demonstrates support for SPE, the origin of this emission remains ambiguous. Specifically, it is unclear whether the emission arises from defects generated by the induced strain or from alternative defect mechanisms. This uncertainty stems from the fluorescence properties inherent to gold, complicating the definitive attribution of the quantum emission source. To provide a rigorous theoretical foundation, the effects of strain are elucidated via the Kirchhoff–Love theory. Additionally, the enhancements observed due to plasmonic effects are comprehensively explained through the resolution of Maxwell's equations. This study will be useful for the development of deterministic and tunable single photonic sources in 2D materials and their integration with plasmonic platforms.
2024
Reyhan Mehta; Anshuman Kumar
Quantum emitters in bilayer hexagonal boron nitride Journal Article
In: arXiv preprint, vol. arXiv:2411.09346, 2024.
@article{arXiv:2411.09346,
title = {Quantum emitters in bilayer hexagonal boron nitride},
author = {Reyhan Mehta and Anshuman Kumar},
url = {https://doi.org/10.48550/arXiv.2411.09346},
doi = {10.48550/arXiv.2411.09346},
year = {2024},
date = {2024-11-15},
urldate = {2024-11-15},
journal = {arXiv preprint},
volume = {arXiv:2411.09346},
abstract = {Hexagonal boron nitride (hBN) has been experimentally shown to exhibit room-temperature single-photon emission. This emission is attributed to defect states in the wide band-gap of hBN, which allow new optical transitions between these dispersion-less defect levels. In this work, we study the new spectral features introduced by interacting atomic defects in consecutive layers of bilayer hBN. Density Functional theory simulations have been carried out to calculate the energy band structure, frequency-dependent complex dielectric functions, and Kohn-Sham states to demonstrate and understand the cause of the emission enhancements. We found that placing colour centres in the vicinity of each other in bilayer hBN introduces new polarization dependent spectral features, with strong dependence on the distance and relative orientation between atomic defects. Our results provide a pathway to engineering single photon emission in hBN via inter-defect interaction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Hexagonal boron nitride (hBN) has been experimentally shown to exhibit room-temperature single-photon emission. This emission is attributed to defect states in the wide band-gap of hBN, which allow new optical transitions between these dispersion-less defect levels. In this work, we study the new spectral features introduced by interacting atomic defects in consecutive layers of bilayer hBN. Density Functional theory simulations have been carried out to calculate the energy band structure, frequency-dependent complex dielectric functions, and Kohn-Sham states to demonstrate and understand the cause of the emission enhancements. We found that placing colour centres in the vicinity of each other in bilayer hBN introduces new polarization dependent spectral features, with strong dependence on the distance and relative orientation between atomic defects. Our results provide a pathway to engineering single photon emission in hBN via inter-defect interaction.
Mahesh Bhupati, Abhishek Mall, Anshuman Kumar, Pankaj K Jha
Deep learning-based variational autoencoder for classification of quantum and classical states of light Journal Article
In: arXiv preprint, vol. arXiv:2405.05243, 2024.
@article{arXiv:2405.05243,
title = {Deep learning-based variational autoencoder for classification of quantum and classical states of light},
author = {Mahesh Bhupati, Abhishek Mall, Anshuman Kumar, Pankaj K Jha},
url = {https://doi.org/10.48550/arXiv.2405.05243},
doi = {10.48550/arXiv.2405.05243},
year = {2024},
date = {2024-05-08},
urldate = {2024-05-08},
journal = {arXiv preprint},
volume = {arXiv:2405.05243},
abstract = {Advancements in optical quantum technologies have been enabled by the generation, manipulation, and characterization of light, with identification based on its photon statistics. However, characterizing light and its sources through single photon measurements often requires efficient detectors and longer measurement times to obtain high-quality photon statistics. Here we introduce a deep learning-based variational autoencoder (VAE) method for classifying single photon added coherent state (SPACS), single photon added thermal state (SPACS), mixed states between coherent/SPACS and thermal/SPATS of light. Our semisupervised learning-based VAE efficiently maps the photon statistics features of light to a lower dimension, enabling quasi-instantaneous classification with low average photon counts. The proposed VAE method is robust and maintains classification accuracy in the presence of losses inherent in an experiment, such as finite collection efficiency, non-unity quantum efficiency, finite number of detectors, etc. Additionally, leveraging the transfer learning capabilities of VAE enables successful classification of data of any quality using a single trained model. We envision that such a deep learning methodology will enable better classification of quantum light and light sources even in the presence of poor detection quality.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Advancements in optical quantum technologies have been enabled by the generation, manipulation, and characterization of light, with identification based on its photon statistics. However, characterizing light and its sources through single photon measurements often requires efficient detectors and longer measurement times to obtain high-quality photon statistics. Here we introduce a deep learning-based variational autoencoder (VAE) method for classifying single photon added coherent state (SPACS), single photon added thermal state (SPACS), mixed states between coherent/SPACS and thermal/SPATS of light. Our semisupervised learning-based VAE efficiently maps the photon statistics features of light to a lower dimension, enabling quasi-instantaneous classification with low average photon counts. The proposed VAE method is robust and maintains classification accuracy in the presence of losses inherent in an experiment, such as finite collection efficiency, non-unity quantum efficiency, finite number of detectors, etc. Additionally, leveraging the transfer learning capabilities of VAE enables successful classification of data of any quality using a single trained model. We envision that such a deep learning methodology will enable better classification of quantum light and light sources even in the presence of poor detection quality.
Kishor Kumar Mandal, Anuj Kumar Singh, Brijesh Kumar, Amit P Shah, Rishabh Vij, Amrita Majumder, Janhavi Jayawant Khunte, Venu Gopal Achanta, Anshuman Kumar
Emission engineering in monolithically integrated silicon nitride microring resonators Journal Article
In: ACS Materials Letters, vol. 6, pp. 1831–1840, 2024.
@article{arXiv:2401.04963,
title = {Emission engineering in monolithically integrated silicon nitride microring resonators},
author = {Kishor Kumar Mandal, Anuj Kumar Singh, Brijesh Kumar, Amit P Shah, Rishabh Vij, Amrita Majumder, Janhavi Jayawant Khunte, Venu Gopal Achanta, Anshuman Kumar},
url = {https://doi.org/10.1021/acsmaterialslett.4c00105},
doi = {10.1021/acsmaterialslett.4c00105},
year = {2024},
date = {2024-04-05},
urldate = {2024-04-05},
journal = {ACS Materials Letters},
volume = {6},
pages = {1831--1840},
abstract = {Monolithic integration of solid-state color centers with photonic elements of the same material is a promising approach to overcome the constraints of fabrication complexity and coupling losses in traditional hybrid integration approaches. A wide band-gap, low-loss silicon nitride (SiN) platform is a mature technology, having CMOS compatibility, widely used in hybrid integrated photonics and optoelectronics. However, it has been shown that certain growth conditions enable the SiN material to host color centers, whose origin is currently under investigation. In this work, we have engineered a novel technique for the efficient coupling of these intrinsic emitters into the whispering gallery modes (WGMs) of the SiN microring cavity -- which has not been explored previously. We have engineered a subwavelength-sized notch into the rim of the SiN microring structure, to optimize the collection efficiency of the cavity-coupled enhanced photoluminescence (PL) spectra at room temperature. The platform presented in this work will enable the development of monolithic integration of color centers with nanophotonic elements for application to quantum photonic technologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Monolithic integration of solid-state color centers with photonic elements of the same material is a promising approach to overcome the constraints of fabrication complexity and coupling losses in traditional hybrid integration approaches. A wide band-gap, low-loss silicon nitride (SiN) platform is a mature technology, having CMOS compatibility, widely used in hybrid integrated photonics and optoelectronics. However, it has been shown that certain growth conditions enable the SiN material to host color centers, whose origin is currently under investigation. In this work, we have engineered a novel technique for the efficient coupling of these intrinsic emitters into the whispering gallery modes (WGMs) of the SiN microring cavity -- which has not been explored previously. We have engineered a subwavelength-sized notch into the rim of the SiN microring structure, to optimize the collection efficiency of the cavity-coupled enhanced photoluminescence (PL) spectra at room temperature. The platform presented in this work will enable the development of monolithic integration of color centers with nanophotonic elements for application to quantum photonic technologies.
2023
Abhay Anand V S, Mihir Kumar Sahoo, Faiha Mujeeb, Abin Varghese, Subhabrata Dhar, Saurabh Lodha, Anshuman Kumar
Novel Nano-Electroplating-Based Plasmonic Platform for Giant Emission Enhancement in Monolayer Semiconductors Journal Article
In: ACS Applied Materials & Interfaces, vol. 15, no. 49, pp. 57783-57790, 2023.
@article{arXiv:2306.13507,
title = {Novel Nano-Electroplating-Based Plasmonic Platform for Giant Emission Enhancement in Monolayer Semiconductors},
author = {Abhay Anand V S, Mihir Kumar Sahoo, Faiha Mujeeb, Abin Varghese, Subhabrata Dhar, Saurabh Lodha, Anshuman Kumar},
url = {https://doi.org/10.1021/acsami.3c11564},
doi = {10.1021/acsami.3c11564},
year = {2023},
date = {2023-12-04},
urldate = {2023-12-04},
journal = {ACS Applied Materials & Interfaces},
volume = {15},
number = {49},
pages = {57783-57790},
abstract = {Two dimensional semiconductors have attracted considerable attention owing to their exceptional electronic and optical characteristics. However, their practical application has been hindered by the limited light absorption resulting from their atomically thin thickness and low quantum yield. A highly effective approach to manipulate optical properties and address these limitations is integrating subwavelength plasmonic nanostructures with these monolayers. In this study, we employed electron beam lithography and electroplating technique to fabricate a gold nanodisc (AuND) array capable of enhancing the photoluminescence (PL) of monolayer MoS2 giantly. Monolayer MoS2 placed on the top of the AuND array yields up to 150-fold PL enhancement compared to that on a gold film. We explain our experimental findings based on electromagnetic simulations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Two dimensional semiconductors have attracted considerable attention owing to their exceptional electronic and optical characteristics. However, their practical application has been hindered by the limited light absorption resulting from their atomically thin thickness and low quantum yield. A highly effective approach to manipulate optical properties and address these limitations is integrating subwavelength plasmonic nanostructures with these monolayers. In this study, we employed electron beam lithography and electroplating technique to fabricate a gold nanodisc (AuND) array capable of enhancing the photoluminescence (PL) of monolayer MoS2 giantly. Monolayer MoS2 placed on the top of the AuND array yields up to 150-fold PL enhancement compared to that on a gold film. We explain our experimental findings based on electromagnetic simulations.
Anuj Kumar Singh, Kishor K Mandal, Yashika Gupta, Abhay Anand VS, Lekshmi Eswaramoorthy, Brijesh Kumar, Abhinav Kala, Saurabh Dixit, Venu Gopal Achanta, Anshuman Kumar
Low-Cost Plasmonic Platform for Photon-Emission Engineering of Two-Dimensional Semiconductors Journal Article
In: Physical Review Applied, vol. 19, no. 4, pp. 044012, 2023.
@article{PhysRevApplied.19.044012,
title = {Low-Cost Plasmonic Platform for Photon-Emission Engineering of Two-Dimensional Semiconductors},
author = {Anuj Kumar Singh, Kishor K Mandal, Yashika Gupta, Abhay Anand VS, Lekshmi Eswaramoorthy, Brijesh Kumar, Abhinav Kala, Saurabh Dixit, Venu Gopal Achanta, Anshuman Kumar},
url = {https://doi.org/10.1103/PhysRevApplied.19.044012},
doi = {10.1103/PhysRevApplied.19.044012},
year = {2023},
date = {2023-04-05},
urldate = {2023-04-05},
journal = {Physical Review Applied},
volume = {19},
number = {4},
pages = {044012},
abstract = {Although the field of 2D materials has democratized materials science by making high quality samples accessible cheaply, due to the atomically thin nature of these systems, an integration with nanostructures is almost always required to obtain a significant optical response. Traditionally, these nanostructures are fabricated via electron beam lithography or focused ion beam milling, which are expensive and large area fabrication can be further time consuming. In order to overcome this problem, we report the integration of 2D semiconductors on a cost-effective and large area fabricated nanocone platform. We show that the plasmon modes of our nanocone structures lead to photoluminescence (PL) enhancement of monolayer WSe2 by about eight to ten times compared to the non-plasmonic case, consistent with finite-difference time-domain simulations. Excitation power-dependent measurements reveal that our nanocone platform enables a versatile route to engineering the relative exciton trion contributions to the emission.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Although the field of 2D materials has democratized materials science by making high quality samples accessible cheaply, due to the atomically thin nature of these systems, an integration with nanostructures is almost always required to obtain a significant optical response. Traditionally, these nanostructures are fabricated via electron beam lithography or focused ion beam milling, which are expensive and large area fabrication can be further time consuming. In order to overcome this problem, we report the integration of 2D semiconductors on a cost-effective and large area fabricated nanocone platform. We show that the plasmon modes of our nanocone structures lead to photoluminescence (PL) enhancement of monolayer WSe2 by about eight to ten times compared to the non-plasmonic case, consistent with finite-difference time-domain simulations. Excitation power-dependent measurements reveal that our nanocone platform enables a versatile route to engineering the relative exciton trion contributions to the emission.
Kishor Kumar Mandal; Yashika Gupta; Brijesh Kumar; Mandar Sohoni; Achanta Venu Gopal; Anshuman Kumar
A photonic integrated chip platform for interlayer exciton valley routing Journal Article
In: Journal of Applied Physics, vol. 133, no. 12, pp. 123104, 2023.
@article{doi:10.1063/5.0139880,
title = {A photonic integrated chip platform for interlayer exciton valley routing},
author = {Kishor Kumar Mandal and Yashika Gupta and Brijesh Kumar and Mandar Sohoni and Achanta Venu Gopal and Anshuman Kumar},
url = {https://doi.org/10.1063/5.0139880},
doi = {10.1063/5.0139880},
year = {2023},
date = {2023-03-30},
urldate = {2023-03-30},
journal = {Journal of Applied Physics},
volume = {133},
number = {12},
pages = {123104},
abstract = {Interlayer excitons in two-dimensional semiconductor heterostructures show suppressed electron–hole overlap resulting in longer radiative lifetimes as compared to intralayer excitons. Such tightly bound interlayer excitons are relevant for important optoelectronic applications, including light storage and quantum communication. Their optical accessibility is, however, limited due to their out-of-plane transition dipole moment. In this work, we design a complementary metal–oxide–semiconductor-compatible photonic integrated chip platform for enhanced near-field coupling of these interlayer excitons with the whispering gallery modes of a microresonator, exploiting the high confinement of light in a small modal volume and high-quality factor of the system. Our platform allows for highly selective emission routing via engineering an asymmetric light transmission that facilitates efficient readout and channeling of the excitonic valley state from such systems.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Interlayer excitons in two-dimensional semiconductor heterostructures show suppressed electron–hole overlap resulting in longer radiative lifetimes as compared to intralayer excitons. Such tightly bound interlayer excitons are relevant for important optoelectronic applications, including light storage and quantum communication. Their optical accessibility is, however, limited due to their out-of-plane transition dipole moment. In this work, we design a complementary metal–oxide–semiconductor-compatible photonic integrated chip platform for enhanced near-field coupling of these interlayer excitons with the whispering gallery modes of a microresonator, exploiting the high confinement of light in a small modal volume and high-quality factor of the system. Our platform allows for highly selective emission routing via engineering an asymmetric light transmission that facilitates efficient readout and channeling of the excitonic valley state from such systems.
2022
Aneesh Bapat; Saurabh Dixit; Yashika Gupta; Tony Low; Anshuman Kumar
Gate tunable light-matter interaction in natural biaxial hyperbolic van der Waals heterostructures Journal Article
In: Nanophotonics, 2022.
@article{arXiv:2110.07526,
title = {Gate tunable light-matter interaction in natural biaxial hyperbolic van der Waals heterostructures},
author = {Aneesh Bapat and Saurabh Dixit and Yashika Gupta and Tony Low and Anshuman Kumar},
url = {https://doi.org/10.1515/nanoph-2022-0034},
doi = {10.1515/nanoph-2022-0034},
year = {2022},
date = {2022-04-04},
urldate = {2022-04-04},
journal = {Nanophotonics},
abstract = {The recent discovery of natural biaxial hyperbolicity in van der Waals crystals, such as α-MoO3, has opened up new avenues for mid-IR nanophotonics due to their deep subwavelength phonon polaritons. However, a significant challenge is the lack of active tunability of these hyperbolic phonon polaritons. In this work, we investigate heterostructures of graphene and α-MoO3 for actively tunable hybrid plasmon phonon polariton modes via electrostatic gating in the mid-infrared spectral region. We observe a unique propagation direction dependent hybridization of graphene plasmon polaritons with hyperbolic phonon polaritons for experimentally feasible values of graphene chemical potential. We further report an application to tunable valley quantum interference in this system with a broad operational bandwidth due to the formation of these hybrid modes. This work presents a lithography-free alternative for actively tunable, anisotropic spontaneous emission enhancement using a sub-wavelength thick naturally biaxial hyperbolic material.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The recent discovery of natural biaxial hyperbolicity in van der Waals crystals, such as α-MoO3, has opened up new avenues for mid-IR nanophotonics due to their deep subwavelength phonon polaritons. However, a significant challenge is the lack of active tunability of these hyperbolic phonon polaritons. In this work, we investigate heterostructures of graphene and α-MoO3 for actively tunable hybrid plasmon phonon polariton modes via electrostatic gating in the mid-infrared spectral region. We observe a unique propagation direction dependent hybridization of graphene plasmon polaritons with hyperbolic phonon polaritons for experimentally feasible values of graphene chemical potential. We further report an application to tunable valley quantum interference in this system with a broad operational bandwidth due to the formation of these hybrid modes. This work presents a lithography-free alternative for actively tunable, anisotropic spontaneous emission enhancement using a sub-wavelength thick naturally biaxial hyperbolic material.
Lekshmi Eswaramoorthy; Sudha Mokkapati; Anshuman Kumar
Engineering Purcell factor anisotropy for dark and bright excitons in two dimensional semiconductors Journal Article
In: Journal of Physics D: Applied Physics, 2022.
@article{arXiv:2108.10680,
title = {Engineering Purcell factor anisotropy for dark and bright excitons in two dimensional semiconductors},
author = {Lekshmi Eswaramoorthy and Sudha Mokkapati and Anshuman Kumar},
url = {https://doi.org/10.1088/1361-6463/ac570e},
doi = {10.1088/1361-6463/ac570e},
year = {2022},
date = {2022-02-21},
urldate = {2022-02-21},
journal = {Journal of Physics D: Applied Physics},
abstract = {Tightly bound dark excitons in atomically thin semiconductors can be used for various optoelectronic applications including light storage and quantum communication. Their optical accessibility is however limited due to their out-of-plane transition dipole moment. We thus propose to strengthen the coupling of dark excitons in two dimensional materials with out-of-plane resonant modes of a cavity at room temperature, by engineering the anisotropy in the Purcell factor. A silica micro-disk characterised by high confinement of light in small modal volume, high Q-factor and free spectral range is used to couple to the excitons in monolayer transition metal dichalcogenides. We show numerically that the tapering of sidewalls of the micro-disk is an extremely versatile route for achieving the selective coupling of whispering gallery modes to light emitted from out-of-plane dipoles to the detriment of that from in-plane ones for four representative monolayer transition metal dichalcogenides.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Tightly bound dark excitons in atomically thin semiconductors can be used for various optoelectronic applications including light storage and quantum communication. Their optical accessibility is however limited due to their out-of-plane transition dipole moment. We thus propose to strengthen the coupling of dark excitons in two dimensional materials with out-of-plane resonant modes of a cavity at room temperature, by engineering the anisotropy in the Purcell factor. A silica micro-disk characterised by high confinement of light in small modal volume, high Q-factor and free spectral range is used to couple to the excitons in monolayer transition metal dichalcogenides. We show numerically that the tapering of sidewalls of the micro-disk is an extremely versatile route for achieving the selective coupling of whispering gallery modes to light emitted from out-of-plane dipoles to the detriment of that from in-plane ones for four representative monolayer transition metal dichalcogenides.
2021
Yongjun Lee, Johnathas D’arf Severo Forte, Andrey Chaves, Anshuman Kumar, Trang Thu Tran, Youngbum Kim, Shrawan Roy, Takashi Taniguchi, Kenji Watanabe, Alexey Chernikov, Joon I. Jang, Tony Low; Jeongyong Kim
Boosting quantum yields in 2D semiconductors via proximal metal plates Journal Article
In: Nature Communications, vol. 12, no. 1, pp. 7095, 2021.
@article{arXiv:2012.15114,
title = {Boosting quantum yields in 2D semiconductors via proximal metal plates},
author = {Yongjun Lee, Johnathas D’arf Severo Forte, Andrey Chaves, Anshuman Kumar, Trang Thu Tran, Youngbum Kim, Shrawan Roy, Takashi Taniguchi, Kenji Watanabe, Alexey Chernikov, Joon I. Jang, Tony Low and Jeongyong Kim },
url = {https://www.nature.com/articles/s41467-021-27418-x},
doi = {10.1038/s41467-021-27418-x},
year = {2021},
date = {2021-12-07},
urldate = {2021-12-07},
journal = {Nature Communications},
volume = {12},
number = {1},
pages = {7095},
abstract = {Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices. However, the short exciton lifetime due to the defect traps and the strong exciton-exciton interaction in TMDs has significantly limited the efficiency of exciton emission from this class of materials. Here, we show that exciton-exciton interaction in 1L-WS2 can be effectively screened using an ultra-flat Au film substrate separated by multilayers of hexagonal boron nitride. Under this geometry, induced dipolar exciton-exciton interaction becomes quadrupole-quadrupole interaction because of effective image dipoles formed within the metal. The suppressed exciton-exciton interaction leads to a significantly improved quantum yield by an order of magnitude, which is also accompanied by a reduction in the exciton-exciton annihilation (EEA) rate, as confirmed by time-resolved optical measurements. A theoretical model accounting for the screening of the dipole-dipole interaction is in a good agreement with the dependence of EEA on exciton densities. Our results suggest that fundamental EEA processes in the TMD can be engineered through proximal metallic screening, which represents a practical approach towards high-efficiency 2D light emitters.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices. However, the short exciton lifetime due to the defect traps and the strong exciton-exciton interaction in TMDs has significantly limited the efficiency of exciton emission from this class of materials. Here, we show that exciton-exciton interaction in 1L-WS2 can be effectively screened using an ultra-flat Au film substrate separated by multilayers of hexagonal boron nitride. Under this geometry, induced dipolar exciton-exciton interaction becomes quadrupole-quadrupole interaction because of effective image dipoles formed within the metal. The suppressed exciton-exciton interaction leads to a significantly improved quantum yield by an order of magnitude, which is also accompanied by a reduction in the exciton-exciton annihilation (EEA) rate, as confirmed by time-resolved optical measurements. A theoretical model accounting for the screening of the dipole-dipole interaction is in a good agreement with the dependence of EEA on exciton densities. Our results suggest that fundamental EEA processes in the TMD can be engineered through proximal metallic screening, which represents a practical approach towards high-efficiency 2D light emitters.
2020
Mandar Sohoni, Pankaj K. Jha, Muralidhar Nalabothula, Anshuman Kumar
Interlayer Exciton Valleytronics in Bilayer Heterostructures Interfaced with a Metasurface Journal Article
In: Applied Physics Letters, vol. 117, no. 12, pp. 121101, 2020.
@article{arXiv:1912.12080,
title = {Interlayer Exciton Valleytronics in Bilayer Heterostructures Interfaced with a Metasurface},
author = {Mandar Sohoni, Pankaj K. Jha, Muralidhar Nalabothula, Anshuman Kumar},
url = {https://doi.org/10.1063/5.0015087},
doi = {10.1063/5.0015087},
year = {2020},
date = {2020-09-21},
urldate = {2020-09-21},
journal = {Applied Physics Letters},
volume = {117},
number = {12},
pages = {121101},
abstract = {The recent proposal of using an anisotropic vacuum for generating valley coherence in transition metal dichalcogenide (TMDC) monolayers has expanded the potential of such valley degrees of freedom for applications in valleytronics. In this work, we open up a completely new regime, inaccessible with monolayer TMDCs, of spontaneously generated valley coherence in interlayer excitons in commensurate TMDC bilayer heterostructures. Using the peculiar out of plane polarization of interlayer excitons in conjunction with an in-plane anisotropic electromagnetic vacuum, we show that a much larger region of the Bloch sphere can be accessible in these heterostructures. We show the accessible phases of these excitons given this in-plane anisotropic electromagnetic vacuum. Our analysis of spontaneous coherence for interlayer excitons may pave the way for engineering an array of interacting quantum emitters in Moiré heterostructures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The recent proposal of using an anisotropic vacuum for generating valley coherence in transition metal dichalcogenide (TMDC) monolayers has expanded the potential of such valley degrees of freedom for applications in valleytronics. In this work, we open up a completely new regime, inaccessible with monolayer TMDCs, of spontaneously generated valley coherence in interlayer excitons in commensurate TMDC bilayer heterostructures. Using the peculiar out of plane polarization of interlayer excitons in conjunction with an in-plane anisotropic electromagnetic vacuum, we show that a much larger region of the Bloch sphere can be accessible in these heterostructures. We show the accessible phases of these excitons given this in-plane anisotropic electromagnetic vacuum. Our analysis of spontaneous coherence for interlayer excitons may pave the way for engineering an array of interacting quantum emitters in Moiré heterostructures.
Feliciano Giustino; Manuel Bibes; Jin Hong Lee; Felix Trier; Roser Valentí; Stephen M. Winter; Young-Woo Son; Louis Taillefer; Christoph Heil; Adriana I. Figueroa; Bernard Plaçais; QuanSheng Wu; Oleg V Yazyev; Erik P A M Bakkers; Jesper Nygård; Pol Forn-Díaz; Silvano de Franceschi; Luis E. F. Foa Torres; James McIver; Anshuman Kumar; Tony Low; Regina Galceran; Sergio O. Valenzuela; Marius Vasile Costache; Aurélien Manchon; Eun-Ah Kim; Gabriel Ravanhani Schleder; Adalberto Fazzio; Stephan Roche
The 2020 Quantum Materials Roadmap Journal Article
In: Journal of Physics: Materials, 2020.
@article{quantum_Materials_Roadmap,
title = {The 2020 Quantum Materials Roadmap},
author = {Feliciano Giustino and Manuel Bibes and Jin Hong Lee and Felix Trier and Roser Valentí and Stephen M. Winter and Young-Woo Son and Louis Taillefer and Christoph Heil and Adriana I. Figueroa and Bernard Plaçais and QuanSheng Wu and Oleg V Yazyev and Erik P A M Bakkers and Jesper Nygård and Pol Forn-Díaz and Silvano de Franceschi and Luis E. F. Foa Torres and James McIver and Anshuman Kumar and Tony Low and Regina Galceran and Sergio O. Valenzuela and Marius Vasile Costache and Aurélien Manchon and Eun-Ah Kim and Gabriel Ravanhani Schleder and Adalberto Fazzio and Stephan Roche},
url = {https://doi.org/10.1088/2515-7639/abb74e},
doi = {10.1088/2515-7639/abb74e},
year = {2020},
date = {2020-09-10},
urldate = {2020-09-10},
journal = {Journal of Physics: Materials},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2018
Cl'ement Javerzac-Galy*; Anshuman Kumar*; Ryan D. Schilling; Nicolas Piro; Sina Khorasani; Matteo Barbone; Ilya Goykhman; Jacob B. Khurgin; Andrea C. Ferrari; Tobias J Kippenberg
Excitonic emission of monolayer semiconductors near-field coupled to high-Q microresonators Journal Article
In: Nano Letters, vol. 18, no. 5, pp. 3138–3146, 2018.
@article{NL_EPFL,
title = {Excitonic emission of monolayer semiconductors near-field coupled to high-Q microresonators},
author = {Cl{'e}ment Javerzac-Galy* and Anshuman Kumar* and Ryan D. Schilling and Nicolas Piro and Sina Khorasani and Matteo Barbone and Ilya Goykhman and Jacob B. Khurgin and Andrea C. Ferrari and Tobias J Kippenberg},
doi = {10.1021/acs.nanolett.8b00749},
year = {2018},
date = {2018-04-06},
urldate = {2018-04-06},
journal = {Nano Letters},
volume = {18},
number = {5},
pages = {3138--3146},
abstract = {We present quantum yield measurements of single layer WSe2 (1L-WSe2) integrated with high-Q (Q > 106) optical microdisk cavities, using an efficient (η > 90
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present quantum yield measurements of single layer WSe2 (1L-WSe2) integrated with high-Q (Q > 106) optical microdisk cavities, using an efficient (η > 90
title = {Tunable Light–Matter Interaction and the Role of Hyperbolicity in Graphene–hBN System},
author = {Anshuman Kumar and Tony Low and Kin Hung Fung and Phaedon Avouris and Nicholas X. Fang},
url = {http://dx.doi.org/10.1021/acs.nanolett.5b01191},
doi = {10.1021/acs.nanolett.5b01191},
year = {2015},
date = {2015-01-01},
urldate = {2015-01-01},
journal = {Nano Letters},
volume = {15},
number = {5},
pages = {3172-3180},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
author = {Anshuman Kumar and Tony Low and Kin Hung Fung and Phaedon Avouris and Nicholas X. Fang},
url = {http://dx.doi.org/10.1021/acs.nanolett.5b01191},
doi = {10.1021/acs.nanolett.5b01191},
year = {2015},
date = {2015-01-01},
urldate = {2015-01-01},
journal = {Nano Letters},
volume = {15},
number = {5},
pages = {3172-3180},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2014
Anshuman Kumar; Kin Hung Fung; M. T. Homer Reid; Nicholas X. Fang
Photon emission rate engineering using graphene nanodisc cavities Journal Article
In: Opt. Express, vol. 22, no. 6, pp. 6400–6415, 2014.
@article{Kumar:14,
title = {Photon emission rate engineering using graphene nanodisc cavities},
author = {Anshuman Kumar and Kin Hung Fung and M. T. Homer Reid and Nicholas X. Fang},
url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-22-6-6400},
doi = {10.1364/OE.22.006400},
year = {2014},
date = {2014-03-01},
urldate = {2014-03-01},
journal = {Opt. Express},
volume = {22},
number = {6},
pages = {6400–6415},
publisher = {OSA},
abstract = {In this work, we present a systematic study of the plasmon modes in a system of vertically stacked pair of graphene discs. Quasistatic approximation is used to model the eigenmodes of the system. Eigen-response theory is employed to explain the spatial dependence of the coupling between the plasmon modes and a quantum emitter. These results show a good match between the semi-analytical calculation and full-wave simulations. Secondly, we have shown that it is possible to engineer the decay rates of a quantum emitter placed inside and near this cavity, using Fermi level tuning, via gate voltages and variation of emitter location and polarization. We highlighted that by coupling to the bright plasmon mode, the radiative efficiency of the emitter can be enhanced compared to the single graphene disc case, whereas the dark plasmon mode suppresses the radiative efficiency.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this work, we present a systematic study of the plasmon modes in a system of vertically stacked pair of graphene discs. Quasistatic approximation is used to model the eigenmodes of the system. Eigen-response theory is employed to explain the spatial dependence of the coupling between the plasmon modes and a quantum emitter. These results show a good match between the semi-analytical calculation and full-wave simulations. Secondly, we have shown that it is possible to engineer the decay rates of a quantum emitter placed inside and near this cavity, using Fermi level tuning, via gate voltages and variation of emitter location and polarization. We highlighted that by coupling to the bright plasmon mode, the radiative efficiency of the emitter can be enhanced compared to the single graphene disc case, whereas the dark plasmon mode suppresses the radiative efficiency.