Research

Fast mid-circuit measurements in a cavity-coupled Ytterbium atom array

PI: Nathan Schine

We aim to address a primary limitation of the well-established neutral atom array architecture, namely fast and local non-destructive mid-circuit measurement. We are building a Ytterbium atom array at the waist of a high finesse optical cavity. Atomic state detection schemes based on this platform improve measurement times by approximately three orders-of-magnitude compared to standard fluorescence detection, and two orders of magnitude compared to schemes limited by atom transport, with direct implications on available circuit depth. This will enable several promising applications including quantum error correction for quantum computation, enhanced optical frequency metrology, and studies of entanglement transitions in interacting spin models.

Learn more: schine.jqi.umd.edu

 

Pound-Drever-Hall Readout of Superconducting Qubits

PI Alicia Kollar

Currently in the circuit QED architecture for superconducting qubits, readout is based on using a homodyne or heterodyne interferometer to sense the frequency of the readout cavity and linear Josephson amplifiers to boost readout signals. The Pound-Drever-Hall (PDH) method, common in the context of optical cavities and lasers, provides an alternative method to sense small changes in a cavity frequency using an off-resonant local oscillator which is co-propagating with the primary probe tone and detected on an E^2 detector. The self-referenced and self-heterodyne nature of this method enable precision sensing of the cavity frequency using a non-quantum-limited detector, even if the probe has poor phase (or path length) stability. Microwave PDH has the potential to enable fast, high-stability qubit readout which is insensitive to clocking stability in the microwave measurement electronics.

Learn more: kollar.jqi.umd.edu

 

Robust cavity metrology beyond the limits of Pound-Drever-Hall

PI Alicia Kollar, Co-PIs Kevin Cox and Nathan Schine

Precise measurement of the resonance frequencies of microwave and optical cavities is a foundational capability across quantum technologies. One of the highest-performance methods currently available is Pound-Drever-Hall (PDH) spectroscopy, which relies on a three-tone interrogation and eliminates sensitivity to path-length fluctuations. However, PDH is known to suffer from systematic offsets due to residual amplitude modulation and demodulation-phase errors. We leverage an optimal linear combination of the phases of the three interrogation tones to implement a method for robust cavity metrology which eliminates significant systematic-error sensitivities of PDH. We experimentally demonstrate robust cavity measurements in both the optical and microwave frequency regime, showing insensitivity to sideband imbalance and demodulation phase, as well as demonstrating single-shot readout of a cavity-coupled superconducting qubit.

Learn more: kollar.jqi.umd.edu

Atoms around optical nanofibers

Co-PIs: Steve Rolston and Frederik Fatemi

We create an efficient atom-photon interface by pulling standard glass optical fibers down to subwavelength scales such that light is no longer completely trapped inside the glass. Instead, a significant portion propagates outside the fiber as an evanescent wave, allowing strong interactions with nearby atoms. In combination with a tunable lattice for trapping neutral atoms near the fiber, this provides a versatile and scalable platform for studying photon-mediated long-range collective interactions and, via its intrinsic connectivity to conventional fiber, provides a significant advantage towards quantum networks.

Learn more: https://jqi.umd.edu/research/research-groups/rolston-research-group

 

Rydberg ensembles for quantum networking

Co-PIs: Steve Rolston and Trey Porto

Our atomic-ensemble system at UMD provides functionality to both generate and store single photons with the requisite characteristics to interface to nodes in a quantum network. Ensembles rely on the almost magic property of spin waves – a single excitation is a symmetric state, with each atom in the ensemble sharing in the excitation and therefore acting like a phased-array antenna that emits with high efficiency into a preferred mode. To create single excitations at high rates, we excite to high-n Rydberg states (up to n = 139), where the Rydberg blockade mechanism prevents a second excitation across the entire ensemble of 1000s of atoms. With this we achieve excellent single-photon fiber-coupled emission with g(2)(0) below 10⁻³ with
rates exceeding 10⁴ s⁻¹ . We are currently exploiting high-fidelity microwave-polarization control for Rydberg ensembles to enhance or suppress Rydberg-Rydberg interactions. 

Learn more: https://jqi.umd.edu/research/research-groups/rolston-research-group and https://porto.jqi.umd.edu/research 

 

The Quantum Frontier of Multi-aperture Sensing

PI Kevin Cox, Co-PI Nathan Schine

We use traditional imaging techniques daily to take pictures of our food, our friends, and our kids (and post them to instagram!). The resolution and signal-to-noise ratio of these images is limited by the laws of classical imaging, such as the famous Rayleigh limit for distinguishing two points. But quantum mechanics tells a different story. In this project we theoretically and experimentally investigate sensing and imaging techniques using multiple apertures at the quantum optima, beyond the limits of classical imaging. We show how quantum resources, such as photonic channels and entanglement, lead to different capabilities from their classical counterparts. This research pioneers a world in which multi-port data is processed using quantum resources in a way that reveals our world in even more exquisite detail.

 

Quantum Processing with spin waves

PI Kevin Cox, Co-PI Nathan Schine

Quantum computing hardware is advancing rapidly, with several important architectures including trapped ions, neutral atom arrays, and superconducting qubits. Most of these platforms focus on storing quantum information as individual qubits. In this research project, we explore a unique way of storing and processing quantum information: as spatial excitation patterns-- called spin waves-- in a cloud of laser-cooled and trapped atoms.  During the covid era, we derived a method to achieve universal quantum computing with spin waves, and now we are embarking upon making this concept a reality. Spin waves offer one particular advantage for networking quantum information. Every spin wave is collecitvely, or superradiantly, enhanced to emit into the same optical fiber. We aim to show how quantum information stored as pattenrs offers unique and powerful alternative perspecitves for the future of quantum technology.

 

Quantum Electrodynamics at Room Temperature

PI Kevin Cox

Rydberg atoms are atoms where one electron is excited to a high energy, large-radius orbital. We have used these atoms to experimentally demonstrate a number of capabilities including building an atomic spectrum analyzer, multi-tone reception, and detecting the k-vector of a radio-frequency field.  Rydberg states are excited using lasers, and the atoms can be created and used at room temperature. Despite all of this project, building sensors that operate at the quantum limit and at room temperature has remained elusive to the field.   In this new project, we pursue this grand goal with full forc. ,By engineering novel microwave resonators and exciting a large number rydberg atoms at their center. We aim to bridge the gap between room-temperature, miniature devices, and devices that operate in the quantum regime. We envision a world where surprising quantum capabilities, such as mode cooling, entanglement generation, and quantum sensing, can be achieved with low size weight and power at room temperature.

 

BIFROST: A first-principles model of polarization mode dispersion in optical fiber

PI Joe Britton Co-PI Steve Rolston

We have developed Bifrost, a first-principles model of polarization mode dispersion (PMD) in optical fibers. This package is designed to connect observed polarization dynamics with underlying physical mechanisms. In 2026 the software was ported to julia and support was added for Monte Carlo modeling, multi-core + SIMD parallelism, first-principles geometric routing and nonlinear scattering in the low-intensity limit.

 

Heterogeneous Quantum Networking between Neutral Atoms and Ions

PI Joseph Britton

A challenge for integration of both ions and Rydberg atoms with high-finesse optical cavities is time varying 
stray charge on the dielectric cavity mirrors. Charge mitigation by use of transparent conductive oxides (TCO) with good DC conductivity like indium-tin-oxide (ITO) and aluminum-doped zinc oxide (AZO) are incompatible as they exhibit unacceptable optical loss. In collaboration with NIST, the Britton Lab formulated a thin-film zinc oxide (ZnO) coating with only 10 ppm additional loss (at 1650 nm) while providing a low surface resistivity at DC ∼ 0.01Ω cm. Relative to ITO and AZO the optical loss is an improvement by ~1000 times. This innovation may enable integration of high-finesse micro-cavities with atomic systems with dramatically higher single-photon cooperativity with reduced dielectric-associated decoherence.