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Nano Letters

Dynamic Quantum Operations at Elevated Temperatures Using Hot-Spot Nanoheating of Color Centers

Frank Bello, Daniel D. A. Clarke, Daniel Wigger, Ortwin G. Hess

Published Aug 28, 2025• 2 citations
Publisher

Abstract

Temperature fluctuations in materials used for quantum networks can give rise to lattice vibrations that detune, dephase, and decrease the lifetimes of embedded quantum defects that function as qubits. Most experiments demonstrating quantum operations have been performed at cryogenic temperatures ranging from milli- to a few kelvin, thereby reducing these adverse effects. However, encouraged by the relatively long lifetimes recently discovered for group IV color centers, we aim to show that subdiffracted heating, i.e., nanoscale thermal "hot spots", produced by a plasmonic transducer can control the resonant behavior of individual qubits. Our analysis, reported over largely unexplored physical dimensions for the nanoheating of qubits, establishes the ability to perform dynamic quantum operations at elevated temperatures via thermally mediated control of two-photon coherence and subsequent photon-number entanglement. As such, color centers raise encouraging prospects for advancing on-chip quantum photonics and elevating solid-state quantum information processing technologies toward higher temperatures.

DOI
10.1021/acs.nanolett.5c04008

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Temperature fluctuations in materials used for quantum networks can give rise to lattice vibrations that detune, dephase, and decrease the lifetimes of embedded quantum defects that function as qubits. Most experiments demonstrating quantum operations have been performed at cryogenic temperatures ranging from milli- to a few kelvin, thereby reducing these adverse effects. However, encouraged by the relatively long lifetimes recently discovered for group IV color centers, we aim to show that subdiffracted heating, i.e., nanoscale thermal "hot spots", produced by a plasmonic transducer can control the resonant behavior of individual qubits. Our analysis, reported over largely unexplored physical dimensions for the nanoheating of qubits, establishes the ability to perform dynamic quantum operations at elevated temperatures via thermally mediated control of two-photon coherence and subsequent photon-number entanglement. As such, color centers raise encouraging prospects for advancing on-chip quantum photonics and elevating solid-state quantum information processing technologies toward higher temperatures.
Photonic quantum networks frequently demand a consistent and reliable source for generating single photons and entangled photon pairs, which function as quintessential encoders of quantum information. However, many experiments demonstrating quantum algorithms using photons have necessarily been performed at cryogenic temperatures (milli to a few Kelvin), in order to mitigate the adverse effects of temperature dephasing. Encouraged by the relatively long lifetimes of group-N color centers, we show that subdiffracted heating produced by a near-field plasmonic transducer can control the resonant behavior of individual quantum emitters and, consequently, their emission. Our theoretical analysis establishes the ability to control antibunching and superbunching effects at elevated temperatures via highly manipulable, thermally-induced strain fields. Furthermore, our work raises encouraging prospects for the application of color centers in on-chip quantum photonics, while elevating technologies for solid-state quantum information processing towards ever higher temperatures.
Achieving dynamic and broadband control of superradiance and subradiance at elevated temperatures is central to quantum photonic technologies. Herein, we theoretically investigate near-field photonics combined with adiabatic and non-adiabatic time-varying media—created via temporal modulation of material properties—to dynamically generate and coherently manipulate quantum emission states, including single photons and photon pairs. Distinctively, this cavity-free near-field method operates effectively at practical temperatures (tens of Kelvin), circumventing traditional operational constraints. We initiate this approach by exploiting plasmonically coupled silicon carbide color centers, which are used as quantum emitters (QEs), with relatively long coherence lifetimes, enabling precise quantum state control before temperature-induced dephasing sets in. In particular, a hybrid plasmonic waveguide is used as the light delivery method, where its subdiffracted near-field generates nanoscale heating that effectively tunes the energies of color centers, via phonon occupation, on resonance with the near-field. Furthermore, we employ transparent conducting oxides, such as indium tin oxide, that may achieve significant refractive index modulation on the femto–picosecond timescales. The resulting behavior is that of a photonic time crystal (PTC) or an epsilon-near-zero (ENZ) material response, dependent on modulation times, and characterized by the amplification or increased absorption of light, respectively, where both enhance field localization around the embedded QEs and extend periods of super- or subradiance compared to static conditions. Our methodology significantly simplifies scalable quantum photonic integration, while advancing quantum memories and entanglement capabilities under accessible conditions.
Group-IV color centers in diamond (SiV, GeV, SnV) have emerged as leading solid-state spin-photon interfaces for quantum information processing applications. However, these qubits require cryogenic temperatures to achieve high fidelity operation due to interactions with the thermal phonon bath. In this work, we: (i) derive a detailed model of the decoherence from first-order acoustic phonon processes acting on the spin-orbit fine structure of these color centers; (ii) demonstrate agreement of the model's predicted coherence times with previous measurements; (iii) identify regimes to suppress phonon-mediated decoherence by changing magnetic-field and strain bias to allow higher temperature operation. This methodology enables prediction of decoherence processes in other color centers and solid-state qubit systems coupled to a thermal bath via a parasitic two-level system. By experiment-anchored decoherence models, we facilitate optimizing qubit coherence for specific applications and devices.
Single-photon emitters in solid-state systems are important building blocks for scalable quantum technologies. Recently, quantum light emitters have been discovered in the wide-gap van der Waals insulator hexagonal boron nitride (hBN). These color centers have attracted considerable attention due to their quantum performance at elevated temperatures and wide range of transition energies. Here, we demonstrate coherent state manipulation of a single hBN color center with ultrafast laser pulses and investigate in our joint experiment–theory study the coupling between the electronic system and phonons. We demonstrate that coherent control can be performed not only resonantly on the optical transition giving access to the decoherence but also phonon-assisted, which reveals the internal phonon quantum dynamics. In the case of optical phonons, we measure their decoherence, stemming in part from their anharmonic decay. Dephasing induced by the creation of acoustic phonons manifests as a rapid decrease in the coherent control signal when traveling phonon wave packets are emitted. Furthermore, we demonstrate that the quantum superposition between a phonon-assisted process and resonant excitation causes ultrafast oscillations of the coherent control signal. Our results pave the way for ultrafast phonon quantum state control on the nanoscale and open up a new promising perspective for hybrid quantum technologies.
Realization of physical systems for quantum information processing fundamentally rests on the ability to generate entanglement among many quantum bits. To this end, solid state quantum systems are often considered a scalable approach due to the relative ease of generating of a large number of individual qubits. However, realizing strong coherent interactions that dominate decoherence processes in the solid state environment is a formidable challenge that has continued to motivate the investigation of new physical systems to store quantum information and new mechanisms to achieve controllable interactions. This thesis takes steps in these directions with diamond color centers, which can store optically accessible quantum information in their electronic spin. We study color center spins as acoustic two level systems, and consider whether their interaction with single phonons in diamond can be engineered to be coherent. Through spectroscopy of color centers in diamond nanomechanical devices and follow-up theoretical work, we identify the negatively charged silicon vacancy (SiV) color center as a promising candidate for phonon-mediated quantum information processing. In the process, an electromechanical device platform capable of tuning the strain environment of color centers is developed. It is used to mitigate thermal decoherence of the SiV spin and demonstrate photon-mediated quantum interference between two SiV centers on a diamond chip, highlighting the utility of nanomechanical devices for photonic quantum networks. Finally, we present high quality factor, wavelength scale acoustic resonators in diamond using phononic crystals towards a coherent interface between SiV centers and single phonons.
Single-photon emitters are fundamental building blocks for quantum information processing, communication and sensing. However, unwanted interactions with bulk phonons in their host environment strongly limit their coherence and controllability. We report single color centers in nanodiamonds that are strongly and comprehensively decoupled from the bulk phononic environment. The color centers feature record-narrow linewidths down to 0.3 nm at room temperature and stable, bright emission, exceeding 10 Mcps in saturation. Notably, the bulk phonon sideband is almost entirely suppressed, revealing the presence of a single localized vibrational mode outside the diamond phonon band. Our observations and simulations point towards a unique mechanism for phonon decoupling in common wide-gap materials, based on a strongly radiative orbital transition coupled to a localized vibrational mode. The new color center enables qualitatively higher performance for applications in quantum networks and nanoscale sensing, and the exploration of new physical resources associated with vibrational states.