arXiv subjects

Elizabeth A. Goldschmidt

Publications and source records attributed to Elizabeth A. Goldschmidt.

At least 19 recordsLinked to original sources

arXiv2026

Compact narrowband photon-pair generation by slow-light spectral engineering

Efficiently generating photon pairs with high heralding efficiency and high single photon purity that are bandwidth matched to quantum emitters, quantum memories, and other matter-based qubits is critical for quantum networking applications. However, nonlinear optics-based sources require substantial spectral engineering to overcome the orders of magnitude bandwidth mismatch between those sources and qubit systems. A popular solution is cavity-enhanced spontaneous parametric down conversion (SPDC) where the cavity sets the photon bandwidth and simultaneously enhances the spectral brightness of the SPDC. Bulk, free-space configurations are generally required to achieve the MHz-scale bandwidths required to interface with most qubit systems. Replicating these in scalable integrated photonic architectures is an ongoing challenge due to the much higher propagation losses that limit the size and linewidth of chip-based resonators. We show here how an intra-cavity slow light medium, acting as an ultra-narrow filter, would enable narrowband photon pair generation in broadband cavities with high single photon purity and without compromising the heralding efficiency. We show that such metrics can be readily realized in erbium doped thin-film lithium niobate microrings using realistic design parameters.

quant-ph↗

arXiv2026

Telecom quantum memory over one microsecond in nanophotonic lithium niobate

Nanophotonic quantum memory is a vital component for scalable quantum information processing for quantum computing, networking, and sensing applications. We store single-photon-level telecom-band optical pulses for more than a microsecond using an atomic frequency comb in erbium-doped thin-film lithium niobate, well beyond what is practically feasible via propagation in even the best nanophotonic devices due to propagation losses. We verify the quantum nature of this storage by demonstrating the phase coherence and sub-single-photon noise upon retrieval. We also show the flexibility of our platform by storing up to 20 temporal modes and demonstrating an acceptance bandwidth up to 2.2 GHz. These results establish erbium-doped thin-film lithium niobate as a practical platform for on-chip quantum memory at telecom wavelengths, a key missing element for photonic quantum computing and quantum networking.

quant-ph↗

arXiv2025

Fidelity and efficiency analysis for heralded entanglement swapping in lossy channels: linear and nonlinear optical approaches

Bell state measurements (BSMs) of photonic qubits are used for quantum networking protocols to herald the distribution and transfer of quantum information. However, standard BSMs based on linear optics (LO-BSMs) require identical photons and are susceptible to errors from multiphoton emissions, leading to reduced fidelity of protocols, particularly in the absence of postselection. To overcome these challenges, Bell state measurements based on nonlinear optics (NLO-BSMs) have been proposed and implemented, leveraging sum-frequency generation (SFG) to filter out multiphoton emissions and improve the fidelity without postselection. Here we analyze the fidelity of LO-BSM and NLO-BSM heralded entanglement swapping in lossy channels and compare their performance under realistic conditions. We also explore the impact of state-of-the-art nonlinear photonics platforms on SFG efficiency and highlight how advances in nanophotonics will enable practical, high-fidelity NLO-BSM-based quantum networking applications.

quant-ph↗

arXiv2025

Ultra High-Q tunable microring resonators enabled by slow light

High-Q nanophotonic resonators are crucial for many applications in classical and quantum optical processing, communication, sensing, and more. We achieve ultra-high quality factors by preparing a highly transparent and strongly dispersive medium within a resonator, causing a reduction in the group velocity that leads to a nearly three order of magnitude increase in the quality factor. We implement this via spectral hole burning in erbium-doped thin-film lithium niobate microring resonators, and show Q-factors exceeding $10^8$. Additionally, we show that the interplay between the spectrally narrowed resonance and the broader bare resonance produces a Fano lineshape, which we dynamically control via electro-optic tuning. Finally, we present a theoretical model for our experimentally observed resonator linewidths, which are not well-described by the standard Bloch equations. Our results show a dramatic reduction in the erbium dephasing rate under a strong optical drive, leading to much narrower linewidths than would otherwise be expected given the large circulating intensity in the resonator.

physics.optics↗

arXiv2025

Heralded photonic graph states with inefficient quantum emitters

Quantum emitter-based schemes for the generation of photonic graph states offer a promising, resource efficient methodology for realizing distributed quantum computation and communication protocols on near-term hardware. We present a heralded scheme for making photonic graph states that is compatible with the typically poor photon collection from state-of-the-art coherent quantum emitters. We demonstrate that the construction time for large graph states can be polynomial in the photon collection efficiency, as compared to the exponential scaling of current emitter-based schemes, which assume deterministic photon collection. The additional overhead here consists of an extra spin qubit plus one additional spin-spin entangling gate per photon added to the graph. While the proposed scheme requires both non-demolition measurement and efficient storage of photons in order to generate graph states for arbitrary applications, we show that many useful tasks, including measurement-based quantum computation, can be implemented without these requirements. As a use-case of our scheme, we construct a protocol for secure two-party computation that can be implemented efficiently on current hardware. Estimates of the fidelity to produce graph states used in the computation are given assuming current and near-term fidelities for highly coherent quantum emitters.

quant-ph↗

arXiv2024

Narrow optical linewidths in stoichiometric layered rare-earth crystals

Rare-earth emitters in solids are well-suited for implementing efficient, long-lived quantum memory coupled to integrated photonics for scalable quantum technologies. They are typically introduced as dopants in a solid-state host, but this introduces disorder and limits the available density of emitters. Stoichiometric materials can offer high densities with narrow optical linewidths. The regular spacing of emitters also opens possibilities for quantum information processing and collective effects. Here we show narrow optical linewidths in a layered stoichiometric crystalline material, NaEu(IO$_3$)$_4$. We observed an inhomogeneous linewidth of 2.2(1) GHz and a homogeneous linewidth of 120(4) kHz. Using spectral hole-burning techniques, we observe a hyperfine spin lifetime of 1.9(4) s. Furthermore, we demonstrate an atomic frequency comb delay of up to 800 ns.

quant-ph↗

arXiv2024

Faithful quantum teleportation via a nanophotonic nonlinear Bell state analyzer

Quantum networking protocols, including quantum teleportation and entanglement swapping, use linear-optical Bell state measurements for heralding the distribution and transfer of quantum information. However, a linear-optical Bell state measurement requires identical photons and is susceptible to errors caused by multiphoton emission, fundamentally limiting the efficiency and fidelity of quantum networking protocols. Here we show a nonlinear Bell state analyzer for time-bin encoded photons based on a nanophotonic cavity with efficient sum-frequency generation to filter multiphoton emissions, and utilize it for faithful quantum teleportation involving spectrally distinct photons with fidelities $\geq 94\%$ down to the single-photon level. Our result demonstrates that nonlinear-optical entangling operations, empowered by our efficient nanophotonics platform, can realize faithful quantum information protocols without requiring identical photons and without the fundamental limit on the efficiency and fidelity of a Bell state measurement imposed by linear optics, which facilitates the realization of practical quantum networks.

quant-ph↗

arXiv2024

Lineshape Optimization in Inhomogeneous $Λ$-type Quantum Memory

Photonic quantum memory is a crucial elementary operation in photonic quantum information processing. While many physically distinct memory protocols and hardware implementations have been applied to this task, the development of a quantum memory performant in all relevant metrics simultaneously (e.g., efficiency, bandwidth, lifetime, etc.) is still an open challenge. In this work, we focus on inhomogeneously broadened ensembles of $Λ$-type quantum emitters, which have long coherence lifetimes and broad bandwidth compatibility, but tend to exhibit low efficiency, in part due to technical constraints on medium growth and preparation, and in part due to inefficient use of a key resource in these systems: the inhomogeneously broadened excited state lineshape. We investigate the properties of electromagnetically induced transparency (EIT) for a survey of inhomogeneous lineshapes that are straightforward to realize experimentally, and optimize the memory efficiency for each lineshape over a large range of experimental parameters. We compare the optimal EIT efficiency to the well-known atomic frequency comb (AFC) protocol, which also relies on spectral shaping of the inhomogeneous broadening, and observe that with sufficient control field power the optimized lineshapes allow more efficient storage. Finally, we optimize over the inhomogeneous lineshape in a protocol agnostic fashion by numerically constructing the linear integral kernel describing the memory interaction and using a singular value decomposition and interpolation procedure to ensure optimality of the resulting lineshape.

quant-ph↗

arXiv2023

Quantum Electrodynamics with Time-varying Dielectrics

We present a framework for quantization of electromagnetic field in the presence of dielectric media with time-varying optical properties. Considering a microscopic model for the dielectric as a collection of matter fields interacting with the electromagnetic environment, we allow for the possibility of dynamically varying light-matter coupling. We obtain the normal modes of the coupled light-matter degrees of freedom, showing that the corresponding creation and annihilation operators obey equal-time canonical commutation relations. We show that these normal modes can consequently couple to quantum emitters in the vicinity of dynamic dielectric media, and the resulting radiative properties of atoms are thus obtained. Our results are pertinent to time-varying boundary conditions realizable across a wide range of state-of-the-art physical platforms and timescales.

quant-ph↗

arXiv2023

Broadband Quantum Memory in Atomic Ensembles

Broadband quantum memory is critical to enabling the operation of emerging photonic quantum technology at high speeds. Here we review a central challenge to achieving broadband quantum memory in atomic ensembles -- what we call the 'linewidth-bandwidth mismatch' problem -- and the relative merits of various memory protocols and hardware used for accomplishing this task. We also review the theory underlying atomic ensemble quantum memory and its extensions to optimizing memory efficiency and characterizing memory sensitivity. Finally, we examine the state-of-the-art performance of broadband atomic ensemble quantum memories with respect to three key metrics: efficiency, memory lifetime, and noise.

quant-ph↗

arXiv2022

Photon echoes using atomic frequency combs in Pr:YSO -- experiment and semiclassical theory

Photon echoes in rare-earth-doped crystals are studied to understand the challenges of making broadband quantum memories using the atomic frequency comb (AFC) protocol in systems with hyperfine structure. The hyperfine structure of Pr^{3+} poses an obstacle to this goal because frequencies associated with the hyperfine transitions change the simple picture of modulation at an externally imposed frequency. The current work focuses on the intermediate case where the hyperfine spacing is comparable to the comb spacing, a challenging regime that has recently been considered. Operating in this regime may facilitate storing quantum information over a larger spectral range in such systems. In this work, we prepare broadband AFCs using optical combs with tooth spacings ranging from 1 MHz to 16 MHz in fine steps, and measure transmission spectra and photon echoes for each. We predict the spectra and echoes theoretically using the optical combs as input to either a rate equation code or a density matrix code, which calculates the redistribution of populations. We then use the redistributed populations as input to a semiclassical theory using the frequency-dependent dielectric function. The two sets of predictions each give a good, but different account of the photon echoes.

quant-ph↗

arXiv2022

Synthesis of Eu(HCOO)$_3$ and Eu(HCOO)$_{3}\cdot$(HCONH$_2$)$_2$ crystals and observation of their $^5$D$_{0}\rightarrow ^{7}$F$_0$ transition for quantum information systems

Two stoichiometric metal-organic frameworks containing Eu$^{3+}$ cations are probed as candidates for photon-based quantum information storage. Synthesis procedures for growing 0.2 mm, rod-shaped Eu(HCOO)$_3$ and 1-3 mm, rhombohedral Eu(HCOO)$_{3}\cdot$(HCONH$_2$)$_2$ single crystals are presented with visible precipitation as soon as 1 h into heating for Eu(HCOO)$_3$ and 24 h for Eu(HCOO)$_{3}\cdot$(HCONH$_2$)$_2$. Room temperature and 1.4 K photoluminescence measurements of the $^5$D$_{0}\rightarrow {^7}$F$_J$ transitions of Eu$^{3+}$ are analyzed for both compounds. Comparisons of peak width and intensity are discussed along with the notable first report for both of the $^5$D$_{0}\rightarrow {^7}$F$_0$ transition, the hyperfine structure of which has potential use in quantum memory applications. The air instability of Eu(HCOO)$_{3}\cdot$(HCONH$_2$)$_2$ and the transformation of its photoluminescence properties are discussed.

cond-mat.mtrl-sci↗

arXiv2021

An atomic frequency comb memory in rare-earth doped thin-film lithium niobate

Atomic frequency combs memories that coherently store optical signals are a key building block for optical quantum computers and quantum networks. Integrating such memories into compact and chip-scale devices is essential for scalable quantum technology, but to date most demonstrations have been in bulk materials or waveguides with large cross-sections, or using fabrication techniques not easily adaptable to wafer scale processing. We demonstrate compact chip-integrated atomic frequency comb storage in rare earth doped thin-film lithium niobate. Our optical memory exhibits a broad storage bandwidth exceeding 100 MHz, and optical storage time of over 250 ns. The enhanced optical confinement in this device structure enables three orders of magnitude reduction in optical power as compared to large ion-diffused waveguides for the same Rabi frequency. These compact atomic frequency comb memories pave the way towards scalable, highly efficient, electro-optically tunable quantum photonic systems that can store and manipulate light on a compact chip.

quant-ph↗

arXiv2021

Tunable quantum interference using a topological source of indistinguishable photon pairs

Sources of quantum light, in particular correlated photon pairs that are indistinguishable in all degrees of freedom, are the fundamental resource that enables continuous-variable quantum computation and paradigms such as Gaussian boson sampling. Nanophotonic systems offer a scalable platform for implementing sources of indistinguishable correlated photon pairs. However, such sources have so far relied on the use of a single component, such as a single waveguide or a ring resonator, which offers limited ability to tune the spectral and temporal correlations between photons. Here, we demonstrate the use of a topological photonic system comprising a two-dimensional array of ring resonators to generate indistinguishable photon pairs with dynamically tunable spectral and temporal correlations. Specifically, we realize dual-pump spontaneous four-wave mixing in this array of silicon ring resonators that exhibits topological edge states. We show that the linear dispersion of the edge states over a broad bandwidth allows us to tune the correlations, and therefore, quantum interference between photons by simply tuning the two pump frequencies in the edge band. Furthermore, we demonstrate energy-time entanglement between generated photons. We also show that our topological source is inherently protected against fabrication disorders. Our results pave the way for scalable and tunable sources of squeezed light that are indispensable for quantum information processing using continuous variables.

physics.optics↗

arXiv2020

On-demand indistinguishable single photons from an efficient and pure source based on a Rydberg ensemble

Single photons coupled to atomic systems have shown to be a promising platform for developing quantum technologies. Yet a bright on-demand, highly pure and highly indistinguishable single-photon source compatible with atomic platforms is lacking. In this work, we demonstrate such a source based on a strongly interacting Rydberg system. The large optical nonlinearities in a blockaded Rydberg ensemble convert coherent light into a single-collective excitation that can be coherently retrieved as a quantum field. We observe a single-transverse-mode efficiency up to 0.18(2), $g^{(2)}=2.0(1.5)\times10^{-4}$, and indistinguishability of 0.982(7), making this system promising for scalable quantum information applications. Accounting for losses, we infer a generation probability up to 0.40(4). Furthermore, we investigate the effects of contaminant Rydberg excitations on the source efficiency. Finally, we introduce metrics to benchmark the performance of on-demand single-photon sources.

quant-ph↗

arXiv2020

Non-Markovian collective emission from macroscopically separated emitters

We study the collective radiative decay of a system of two two-level emitters coupled to a one-dimensional waveguide in a regime where their separation is comparable to the coherence length of a spontaneously emitted photon. The electromagnetic field propagating in the cavity-like geometry formed by the emitters exerts a retarded backaction on the system leading to strongly non-Markovian dynamics. The collective spontaneous emission rate of the emitters exhibits an enhancement or inhibition beyond the usual Dicke super- and sub-radiance due to a self-consistent coherent time-delayed feedback.

quant-ph↗

arXiv2019

Electromagnetically induced transparency in inhomogeneously broadened solid media

We study, theoretically and experimentally, electromagnetically induced transparency (EIT) in two different solid-state systems. Unlike many implementations in homogeneously broadened media, these systems exhibit inhomogeneous broadening of their optical and spin transitions typical of solid-state materials. We observe EIT lineshapes typical of atomic gases, including a crossover into the regime of Autler-Townes splitting, but with the substitution of the inhomogeneous widths for the homogeneous values. We obtain quantitative agreement between experiment and theory for the width of the transparency feature over a range of optical powers and inhomogeneous linewidths. We discuss regimes over which analytical and numerical treatments capture the behavior. As solid-state systems become increasingly important for scalable and integratable quantum optical and photonic devices, it is vital to understand the effects of the inhomogeneous broadening that is ubiquitous in these systems. The treatment presented here can be applied to a variety of systems, as exemplified by the common scaling of experimental results from two different systems.

quant-ph↗

arXiv2019

An Integrated Photonic Platform for Rare-Earth Ions in Thin Film Lithium Niobate

Rare-earth ion ensembles doped in single crystals are a promising materials system with widespread applications in optical signal processing, lasing, and quantum information processing. Incorporating rare-earth ions into integrated photonic devices could enable compact lasers and modulators, as well as on-chip optical quantum memories for classical and quantum optical applications. To this end, a thin film single crystalline wafer structure that is compatible with planar fabrication of integrated photonic devices would be highly desirable. However, incorporating rare-earth ions into a thin film form-factor while preserving their optical properties has proven challenging. We demonstrate an integrated photonic platform for rare-earth ions doped in a single crystalline thin film on insulator. The thin film is composed of lithium niobate doped with Tm3+. The ions in the thin film exhibit optical lifetimes identical to those measured in bulk crystals. We show narrow spectral holes in a thin film waveguide that require up to 2 orders of magnitude lower power to generate than previously reported bulk waveguides. Our results pave way for scalable on-chip lasers, optical signal processing devices, and integrated optical quantum memories.

physics.optics↗