arXiv subjects

Emanuel Green

Publications and source records attributed to Emanuel Green.

4 recordsLinked to original sources

arXiv2025

Sub-second spin and lifetime-limited optical coherences in $^{171}$Yb$^{3+}$:CaWO$_4$

Optically addressable solid-state spins have been extensively studied for quantum technologies, offering unique advantages for quantum computing, communication, and sensing. Advancing these applications is generally limited by finding materials that simultaneously provide lifetime-limited optical and long spin coherences. Here, we introduce $^{171}$Yb$^{3+}$ ions doped into a CaWO$_4$ crystal. We perform high-resolution spectroscopy of the excited state, and demonstrate all-optical coherent control of the electron-nuclear spin ensemble. We find narrow inhomogeneous broadening of the optical transitions of 185 MHz and radiative-lifetime-limited coherence time up to 0.75~ms. Next to this, we measure a spin-transition ensemble line width of 5 kHz and electron-nuclear spin coherence time reaching 0.15~seconds at zero magnetic field between 50~mK and 1~K temperatures. These results demonstrate the potential of $^{171}$Yb$^{3+}$:CaWO$_4$ as a low-noise platform for building quantum technologies with ensemble-based memories, microwave-to-optical transducers, and optically addressable single-ion spin qubits.

quant-ph↗

arXiv2024

Multiplexed Entanglement of Multi-emitter Quantum Network Nodes

Quantum networks that distribute entanglement among remote nodes will unlock transformational technologies in quantum computing, communication, and sensing. However, state-of-the-art networks utilize only a single optically-addressed qubit per node; this constrains both the quantum communication bandwidth and memory resources, greatly impeding scalability. Solid-state platforms provide a valuable resource for multiplexed quantum networking where multiple spectrally-distinguishable qubits can be hosted in nano-scale volumes. Here we harness this resource by implementing a two-node network consisting of several rare-earth ions coupled to nanophotonic cavities. This is accomplished with a protocol that entangles distinguishable 171Yb ions through frequency-erasing photon detection combined with real-time quantum feedforward. This method is robust to slow optical frequency fluctuations occurring on timescales longer than a single entanglement attempt: a universal challenge amongst solid-state emitters. We demonstrate the enhanced functionality of these multi-emitter nodes in two ways. First, we mitigate bottlenecks to the entanglement distribution rate through multiplexed entanglement of two remote ion pairs. Secondly, we prepare multipartite W-states comprising three distinguishable ions as a resource for advanced quantum networking protocols. These results lay the groundwork for scalable quantum networking based on rare-earth ions.

quant-ph↗

arXiv2022

Delicate Ferromagnetism in MnBi$_6$Te$_{10}$

Tailoring magnetic orders in topological insulators is critical to the realization of topological quantum phenomena. An outstanding challenge is to find a material where atomic defects lead to tunable magnetic orders while maintaining a nontrivial topology. Here, by combining magnetization measurements, angle-resolved photoemission spectroscopy, and transmission electron microscopy, we reveal disorder-enabled, tunable magnetic ground states in MnBi$_6$Te$_{10}$. In the ferromagnetic phase, an energy gap of 15 meV is resolved at the Dirac point on the MnBi$_2$Te$_4$ termination. In contrast, antiferromagnetic MnBi$_6$Te$_{10}$ exhibits gapless topological surface states on all terminations. Transmission electron microscopy and magnetization measurements reveal substantial Mn vacancies and Mn migration in ferromagnetic MnBi$_6$Te$_{10}$. We provide a conceptual framework where a cooperative interplay of these defects drives a delicate change of overall magnetic ground state energies, and leads to tunable magnetic topological orders. Our work provides a clear pathway for nanoscale defect-engineering towards the realization of topological quantum phases.

cond-mat.mtrl-sci↗

arXiv2021

An Integrated Quantum Material Testbed with Multi-Resolution Photoemission Spectroscopy

We present the development of a multi-resolution photoemission spectroscopy (MRPES) setup which probes quantum materials in energy, momentum, space, and time. This versatile setup integrates three light sources in one photoemission setup, and can conveniently switch between traditional angle-resolved photoemission spectroscopy (ARPES), time-resolved ARPES (trARPES), and micron-scale spatially resolved ARPES ($μ$ARPES). It provides a first-time all-in-one solution to achieve an energy resolution $< 4$ meV, a time resolution $< 35$ fs, and a spatial resolution $\sim 10$ $μ$m in photoemission spectroscopy. Remarkably, we obtain the shortest time resolution among the trARPES setups using solid-state nonlinear crystals for frequency upconversion. Furthermore, this MRPES setup is integrated with a shadow-mask assisted molecular beam epitaxy system, which transforms the traditional photoemission spectroscopy into a quantum device characterization instrument. We demonstrate the functionalities of this novel quantum material testbed using FeSe/SrTiO$_3$ thin films and MnBi$_4$Te$_7$ magnetic topological insulators.

physics.ins-det↗