arXiv subjects

Imran M. Mirza

Publications and source records attributed to Imran M. Mirza.

At least 19 recordsLinked to original sources

arXiv2026

Mapping photon-number regimes in single-emitter lasers

Cavity quantum electrodynamics (cQED) architectures are known to produce traditional laser signatures from a coherently driven single quantum emitter. In this paper, we present a numerical analysis of an open quantum system consisting of an incoherently pumped three-level emitter strongly coupled to a single cavity mode. In particular, we focus on three cavity photon-number ($n_p$) regimes modeled within a truncated Hilbert space of dimension up to $N=51$: deep quantum ($n_p \leq 1$), intermediate quantum ($2 \leq n_p \leq 50$), and semi-classical ($n_p \gg 50$). We investigate the photon threshold for entering the lasing regime while completely bypassing the requirement for a coherent drive, revealing that laser behavior can emerge from minimal photon populations. For example, by solving the Lindblad master equation, we find that lasing stabilizes in the intermediate quantum regime where stimulated emission dominates spontaneous emission. We further observe sub-Poissonian photon statistics in this regime, as confirmed by a donut-like Wigner distribution, near-unity second-order coherence function $g^{(2)}(0) \approx 1$, and a minimized Mandel $Q$-parameter. However, within the range $10 < n_p < 50$, we observe a loss of coherence at higher incoherent pumping rates, leading to self-quenching. In the semi-classical regime ($n_p \gg 50$), treated under a mean-field approximation for our choice of system parameters, we find that the laser quenches at an incoherent pumping rate of $Γ\approx 65$ (in units of the atomic decay rate $γ_{12}$). Our findings can be applied to define the operational limits of single-emitter light sources, thereby providing useful guidelines for the development of nanolasers and scalable quantum networks.

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arXiv2026

Chirality-free photon routing via giant atoms in waveguide QED ladders

In this paper, we present an in-depth examination of single-photon routing in a multi-emitter waveguide quantum electrodynamics ladder with up to five giant atoms simultaneously coupled across two linear waveguides. Using a real-space approach, we analyze a non-chiral routing architecture and evaluate the impact of scaling the number of giant atoms in three topologically distinct configurations: fully separated, simply braided, and fully nested. Using numerical results, we show that increasing the number of giant atoms, in separate or braided configurations, greatly expands the operational parameter space for near-deterministic ($\sim$100%) photon routing into the target waveguide, achieving directionality through quantum interference alone. In contrast, the nested architecture is limited to a maximum routing efficiency of 25% due to rigid geometric symmetries, although this limitation could be mitigated by employing less symmetric coupling distances. Finally, we assess the system under direct interatomic interactions and environmental dissipation. Our results show that, while spontaneous emission reduces transport probabilities, the multi-atom-separated configuration maintains high routing efficiencies across broad operational windows of incoming photon frequency without requiring chiral coupling.

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arXiv2025

Exploring Photon Blockade in Multimode Jaynes-Cummings Models with Two-Photon Dissipation

The photon blockade phenomenon, a promising tool for realizing efficient single-photon sources, is the central focus of our work. We study this phenomenon within the context of the multimode extension of the Jaynes-Cummings model, incorporating two-photon dissipation and external coherent driving. Operating in the weak-driving regime, we confine our analysis to the two-excitation sector of the Hilbert space, initially exploring the single-mode case and then focusing on the corresponding multimode problem. Our study calculates the second-order correlation function (both numerically and analytically) for zero- and nonzero time delays in single- and multimode cases, to pinpoint and validate the conditions that lead to conventional and unconventional photon blockade. Our zero delay findings reveal that photon antibunching is comparable in both cases; however, the multimode case offers a greater degree of control and applicability. Furthermore, for non-zero delay operation, we find that when one of the multiple modes is set at the optimal conventional photon blockade conditions, the behavior of the curve mimics the single-mode problem with an overall slower rate of reaching the $g^{(2)}(τ)=1$ value. These results highlight the practical implications of our findings for building useful single-photon sources.

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arXiv2025

Tripartite Entanglement in Multimode Cavity Quantum Electrodynamics

We numerically investigate the generation and dynamics of tripartite entanglement among qubits (quantum emitters or atoms) in multimode cavity quantum electrodynamics (cQED). Our cQED architecture features three initially unentangled excited two-level quantum emitters confined within a triangle-shaped multimode optical cavity, which later become entangled due to a Jaynes-Cummings-like interaction. Using the tripartite negativity measure of entanglement and fidelity with respect to the genuine tripartite entangled state (Greenberger-Horne-Zeilinger (or GHZ) state, to be precise), we analyze the impact of the number of cavity modes, qubit locations, and losses (spontaneous emission from qubits and photon leakage from the cavity mirrors) on the generated entanglement. Our key results include the presence of two kinds of retardation effects: one resulting from the time it takes for photons to propagate from one qubit to another, and the other to complete one round trip in the cavity. We observed these retardation effects only in multimode cavities, with the exciting possibility of controlling the collapse and revival patterns of tripartite entanglement by altering the qubit locations in the cavity. Furthermore, the impact of losses on the generated entanglement and the dependence of maximum entanglement on the total number of modes yield results that surpass those reported for single and two excitations. With recent advances in circuit quantum electrodynamics, these findings hold promise for the development of entanglement-based quantum networking protocols and quantum memories.

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arXiv2025

Hong-Ou-Mandel interferometry with cavity QED-based single-photon sources: A Quantum Jump Analysis

We present a quantum jump/trajectory analysis of the two-photon interference phenomenon in the context of the Hong-Ou-Mandel effect (HOME). In particular, we consider the standard setup of HOME, which consists of two-photon sources firing single photons from the opposite sides of a 50/50 beam splitter and two perfect detectors placed at the output ports to record photodetection events. For single-photon sources, we consider two special cases: (1) two excited two-level atoms and (2) two atom-cavity setups with initially present single photons in both cavities. For both cases, we report analytic results as well as quantum jump-based Monte Carlo simulations to demonstrate the signatures of these single-photon sources on the HOME under different working conditions (for example, strong- and weak-coupling regimes of cavity quantum electrodynamics). Our results may have interesting applications in linear optics quantum computing as well as in protocols that test the indistinguishability of single-photon sources.

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arXiv2024

Photon routing in disordered chiral waveguide QED ladders: Interplay between photonic localization and collective atomic effects

In recent years, photon routing has garnered considerable research activity due to its key applications in quantum networking and optical communications. This paper studies the single photon routing scheme in many-emitter disordered chiral waveguide quantum electrodynamics (wQED) ladders. The wQED ladder consists of two one-dimensional lossless waveguides simultaneously and chirally coupled with a chain of dipole-dipole interacting two-level quantum emitters (QEs) or atoms. In particular, we analyze how a departure from the periodic placement of the QEs due to temperature-induced position disorder can impact the routing probability. This involves analyzing how the interplay between the collective atomic effects originating from the dipole-dipole interaction and disorder in the atomic location leading to single-photon localization can change the routing probabilities. As for some key results, we find that the routing probability exhibits a considerable improvement (more than $90\%$ value) for periodic and disordered wQED ladders when considering lattices consisting of twenty QEs. This robustness of collective effects against spontaneous emission loss and weak disorders is further confirmed by examining the routing efficiency and localization length for up to twenty QE chains. These results may find applications in quantum networking and distributed quantum computing under the realistic conditions of imperfect emitter trappings.

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arXiv2024

Band Gap Engineering and Controlling Transport Properties of Single Photons in Periodic and Disordered Jaynes-Cummings Arrays

We theoretically study the single photon transport properties in periodic and position-disordered Jaynes-Cummings (or JC) arrays of waveguide-coupled microtoroidal ring resonators, each interacting with a single two-level quantum emitter. Employing the real-space formalism of quantum optics, we focus on various parameter regimes of cavity quantum electrodynamics (cQED) to gain better control of single photon propagation in such a many-body quantum optical setting. As for some of the key findings, we observe that the periodic setting leads to the formation of the band structure in the photon transmission spectra, which is most evident in the strong coupling regime of cQCD. However, under the resonant conditions with no losses, the application of Bloch's theorem indicates that the width of forbidden gaps can be altered by tuning the emitter-cavity coupling to small values. Moreover, in the disordered case, we find that the single photon transmission curves show the disappearance of band formation. However, spectral features originating from cQED interactions observed for single atom-cavity problem remain robust against weak-disordered conditions. The results of this work may find application in the study of quantum many-body effects in the optical domain as well as in different areas of quantum computation and quantum networking.

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arXiv2023

Chirality-assisted enhancement of tripartite entanglement in waveguide QED

We study the generation and control of genuine tripartite entanglement among quantum emitters (QEs) that are side coupled to one-dimensional spin-momentum locked (or chiral) waveguides. By applying the machinery of Fock state master equations along with the recently proposed concurrence fill measure of tripartite entanglement [S. Xie and J. H. Eberly, Phys. Rev. Lett. 127, 040403 (2021)], we analyze how three-photon Gaussian wavepackets can distribute entanglement among two and three QEs. We show that with a five times larger waveguide decay rate in the right direction as compared to the left direction, the maximum value of tripartite entanglement can be elevated by 35% as compared to the symmetric scenario where both left and right direction decay rates are equal. Additionally, chirality can maintain the tripartite entanglement for longer times in comparison to the corresponding symmetric decay rate situation. Finally, we study the influence of detunings and spontaneous emission on the resulting entanglement. We envision quantum networking and long-distance quantum communication as two main areas of applications of this work.

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arXiv2023

Electromagnetically induced transparency in many-emitter waveguide quantum electrodynamics: linear versus nonlinear waveguide dispersions

We study single-photon induced electromagnetically induced transparency (EIT) in many-emitter waveguide quantum electrodynamics (wQED) with linear and nonlinear waveguide dispersion relations. In the single-emitter problem, in addition to the robustness of the EIT spectral features in the over-coupled regime of wQED, we find that the nonlinear dispersion results in the appearance of a side peak for frequencies smaller than the resonant EIT frequency which turns into a pronounced plateau as the nonlinearity is enhanced. Consequently, for many-emitter scenarios, our results indicate the formation of band structure which for higher values of nonlinearity leads to narrow band gaps as compared to the corresponding linear dispersion case. Long-distance quantum networking aided with quantum memories can serve as one of the targeted applications of this work.

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arXiv2023

Nonreciprocal slow or fast light in anti-$\mathcal{PT}$-symmetric optomechanics

Non-Hermitian systems with anti-parity-time ($\mathcal{APT}$) symmetry have revealed rich physics beyond conventional systems. Here, we study optomechanics in an $\mathcal{APT}$-symmetric spinning resonator and show that, by tuning the rotating speed to approach the exceptional point (EP) or the non-Hermitian spectral degeneracy, nonreciprocal light transmission with a high isolation ratio can be realized. Accompanying this process, nonreciprocal group delay or advance is also identified in the vicinity of EP. Our work sheds new light on manipulating laser propagation with optomechanical EP devices and, in a broader view, can be extended to explore a wide range of $\mathcal{APT}$-symmetric effects, such as $\mathcal{APT}$-symmetric phonon lasers, $\mathcal{APT}$-symmetric topological effects, and $\mathcal{APT}$-symmetric force sensing or accelerator.

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arXiv2022

Engineering Optomechanically Induced Transparency by coupling a qubit to a spinning resonator

We theoretically study the spectral properties of a pump-probe driven hybrid spinning optomechanical ring resonator optically coupled with a two-level quantum emitter (QE or qubit). Recently we have shown [arXiv:1810.03709] that in the absence of the emitter the coupled cavity version of this setup is not only capable of nonreciprocal light propagation but can also exhibit slow & fast light propagation. In this work, we investigate in what ways the presence of a single QE coupled with the optical whispering gallery modes of the spinning optomechanical resonator can alter the probe light nonreciprocity. Under the weak-excitation assumption and mean-field approximation, we find that the interplay between the rotational/spinning Sagnac-effect and the qubit coupling can lead to the enhancement both in the optomechanically induced transparency (OMIT) peak value and in the width of the transparency window due to the opening of qubit-assisted back reflection channel. However, compared to the no-qubit case, we notice that such an enhancement comes at the cost of degrading the group delay in probe light transmission by a factor of 1/2 for clockwise rotary directions. The target applications of these results can be in the areas of quantum circuitry and in non-reciprocal quantum communication protocols where QEs are a key component.

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arXiv2022

Non-Markovianity in photosynthetic reaction centers: A noise-induced quantum coherence perspective

The long-standing problem of nearly perfect photosynthetic yield in some types of bacteria and nearly all kinds of plants despite the interaction with a hot and noisy environment has witnessed quantum optical explanations in the last decade or so. Typically in these explanations, photosynthetic reaction centers are modeled as five-level quantum heat engines where the generation of Fano-type interference due to the coupling of discrete state transitions with a common Markovian reservoir is held responsible for the enhancement of the photosynthetic efficiency. In this work, we go beyond the Born-Markov approximation used in the earlier works and study the impact of non-Markovian environments with Lorentzian spectral densities on the dynamics of light-harvesting complexes.

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arXiv2021

On the dissipative dynamics of entangled states in coupled-cavity quantum electrodynamics arrays

We examine the dissipative dynamics of N00N states with an arbitrary photon number N in two architectures of fiber-coupled optical ring resonators (RRs) interacting with two-level quantum emitters. One architecture consists of a two-way cascaded array of emitter-cavity systems, while in the other architecture we consider two fiber-coupled RRs each coupled to multiple dipole-dipole interacting (DDI) quantum emitters (QEs). Our focus in this paper is to study how am initially prepared multiple excitation atomic N00N states transfers to the RRs and then how rapidly it decays in these open cavity quantum electrodynamics (CQED) setups while varying the emitter-cavity coupling strengths, emitter-cavity detuning, and backscattering from cavity modes. We present a general theoretical formalism valid for any arbitrary numbers of QEs, RRs, and N number in the N00N state for both schemes. As examples, we discuss the cases of single and two-excitation N00N states and report the comparison of our findings in both schemes. As one of the main results, we conclude that the array scheme tends to store N00N for longer times while the DDI scheme supports higher fidelity values. The results of this study may find applications in designing new multiparty entanglement-based protocols in quantum metrology and quantum lithography.

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arXiv2021

Coherent Perfect Absorption in Tavis-Cummings Models

We theoretically study the conditions under which two laser fields can undergo Coherent Perfect Absorption (CPA) when shined on a single-mode bi-directional optical cavity coupled with two two- level quantum emitters (natural atoms, artificial atoms, quantum dots, qubits, etc.). In addition to being indirectly coupled through the cavity-mediated field, in our Tavis-Cummings model the two quantum emitters (QEs) are allowed to interact directly via the dipole-dipole interaction (DDI). Under the mean-field approximation and low-excitation assumption, in this work, we particularly focus on the impact of DDI on the existence of CPA in the presence of decoherence mechanisms (spontaneous emission from the QEs and the leakage of photons from the cavity walls). We also present a dressed-state analysis of the problem to discuss the underlying physics related to the allowed polariton state transitions in the Jaynes-Tavis-Cummings ladder. As a key result, we find that in the strong-coupling regime of cavity quantum electrodynamics, the strong DDI and the emitter-cavity detuning can act together to achieve the CPA at two laser frequencies tunable by the inter-atomic separation which are not possible to attain with a single QE in the presence of detuning. Our CPA results are potentially applicable in building quantum memories that are an essential component in long-distance quantum networking.

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arXiv2020

Collective photon routing improvement in a dissipative quantum emitter chain strongly coupled to a chiral waveguide QED ladder

We examine the routing scheme of single photons in a one-dimensional periodic chain of two-level quantum emitters (QEs) strongly coupled to two waveguides in a ladder configuration. It is known that for a single-emitter chiral waveguide ladder setting, photons can be redirected from one waveguide to another with a $100\%$ probability (deterministically) provided the resonance condition is met and spontaneous emission is completely ignored. However, when the spontaneous emission is included the routing scheme becomes considerably imperfect. In this paper, we present a solution to this issue by considering a chain of QEs where in addition to the waveguide mediated interaction among emitters, a direct and infinitely long-ranged dipole-dipole interaction (DDI) is taken into account. We show that the collective effects arising from the strong DDI protect the routing scheme from spontaneous emission loss. In particular, we demonstrate that the router operation can be improved from $58\%$ to $95\%$ in a typical dissipative chiral light-matter interface consisting of nanowires modes strongly interacting with a linear chain of 30 quantum dots. With the recent experimental progress in chiral quantum optics, trapped QEs evanescently coupled to tapered nanofibers can serve as a platform for the experimental realization of this work.

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arXiv2018

On the optical nonreciprocity and slow light propagation in coupled spinning optomechanical resonators

We study the optical transmission characteristics of pump-probe driven spinning optomechanical ring resonators coupled in a series configuration. After performing the steady-state analysis valid for an arbitrary number of resonators, as an example, we discuss the two-resonator problem in detail. Therein, we focus on how changing the optical Sagnac effect due to same or opposite spinning directions of resonators can lead to enhanced, non-reciprocal and delayed probe light transmission. This work can help in devising spin degree of freedom based novel devices of manipulating light propagation in quantum networks and quantum communication technologies.

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arXiv2018

Dimer chains in waveguide quantum electrodynamics

We examine the propagation of single photons in periodic and disordered dimer chains coupled to one-dimensional chiral and bidirectional waveguides. Each dimer is composed of two dipole-coupled atoms. In the disordered setting, we separately treat two types of position disorder, namely in dimer length and in dimer separation. The focus of this study is to understand in what ways the interplay between dipole-dipole interactions and directionality of photon emission can impact the transport of single photons. Cold atoms trapped near optical fibers can serve as an experimentally realizable platform for the models that we consider.

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arXiv2017

Influence of Disorder on Electromagnetically Induced Transparency in Chiral Waveguide Quantum Electrodynamics

We study single photon transport in a one-dimensional disordered lattice of three-level atoms coupled to an optical waveguide. In particular, we study atoms of Λ-type that are capable of exhibiting electromagnetically induced transparency (EIT) and separately consider disorder in the atomic positions and transition frequencies. We mainly address the question of how preferential emission into waveguide modes (chirality) can influence the formation of spatially localized states. Our work has relevance to experimental studies of cold atoms coupled to nanoscale waveguides and has possible applications to quantum communications.

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