One central theme in quantum photonics is tailoring the interactions between atoms/spins and their electromagnetic (EM) environments. Considerable effort has focused on engineering spontaneous emission by shaping EM environments, known as the Purcell effect. However, photonic environment control of pure dephasing, which is a complementary paradigm of non-unitary atom/spin couplings with EM environments, remains largely unexplored. Here, we introduce a nanophotonic approach to modify qubit pure dephasing dynamics. Unlike Purcell engineering that tailors photonic environments at qubit resonance frequencies (typically optical/near-infrared), we develop ultra-subwavelength spin noise metasurfaces for efficient broadband control of low-frequency (e.g., $\sim$MHz) photonic environments far off-resonant with atoms/spins for dephasing engineering. We experimentally demonstrate our approach using lithographically defined CoFeB metasurfaces and shallow nitrogen-vacancy (NV) centers in diamond. Instead of modified spontaneous emission, we observe modified NV pure dephasing dynamics near different spin noise metasurfaces. We further isolate metasurface-controlled dephasing from other dephasing mechanisms (e.g., spin bath) by measuring the NV ensemble dephasing noise spectrum with dynamical decoupling spectral decomposition techniques. Our results establish a new frontier in engineering quantum light-matter interactions with nanophotonic structures.
One central theme in quantum photonics is tailoring the interactions between atoms/spins and their electromagnetic (EM) environments. Considerable effort has focused on engineering spontaneous emission by shaping EM environments, known as the Purcell effect. However, photonic environment control of pure dephasing, which is a complementary paradigm of non-unitary atom/spin couplings with EM environments, remains largely unexplored. Here, we introduce a nanophotonic approach to modify qubit pure dephasing dynamics. Unlike Purcell engineering that tailors photonic environments at qubit resonance frequencies (typically optical/near-infrared), we develop ultra-subwavelength spin noise metasurfaces for efficient broadband control of low-frequency (e.g., ∼MHz) photonic environments far off-resonant with atoms/spins for dephasing engineering. We experimentally demonstrate our approach using lithographically defined CoFeB metasurfaces and shallow nitrogen-vacancy (NV) centers in diamond. Instead of modified spontaneous emission, we observe modified NV pure dephasing dynamics near different spin noise metasurfaces. We further isolate metasurface-controlled dephasing from other dephasing mechanisms (e.g., spin bath) by measuring the NV ensemble dephasing noise spectrum with dynamical decoupling spectral decomposition techniques. Our results establish a new frontier in engineering quantum light-matter interactions with nanophotonic structures.
One central theme in quantum photonics is tailoring the interactions between atoms/spins and their electromagnetic (EM) environments. Considerable effort has focused on engineering spontaneous emission by shaping EM environments, known as the Purcell effect. However, photonic environment control of pure dephasing, which is a complementary paradigm of non-unitary atom/spin couplings with EM environments, remains largely unexplored. Here, we introduce a nanophotonic approach to modify qubit pure dephasing dynamics. Unlike Purcell engineering that tailors photonic environments at emitter transition frequencies (typically optical/near-infrared), we develop ultra-subwavelength spin noise metasurfaces for efficient broadband control of low-frequency (∼MHz) photonic environments far off-resonant with atom/spin transitions for dephasing engineering. We experimentally demonstrate our approach using lithographically defined CoFeB metasurfaces and shallow nitrogen-vacancy (NV) centers in diamond. Instead of modified spontaneous emission, we observe modified NV pure dephasing dynamics near different spin noise metasurfaces. We further isolate metasurface-controlled dephasing from other dephasing mechanisms (e.g., spin bath) by measuring the NV ensemble dephasing noise spectrum with dynamical decoupling spectral decomposition techniques. Our results establish, to our knowledge, a new frontier in engineering quantum light–matter interactions with nanophotonic structures.
Pure dephasing and spontaneous emission are two nonunitary processes of atoms or spins interacting with fluctuating electromagnetic (EM) modes. The dissipative collective emission processes (e.g., superradiance) originate from interactions with EM modes in resonance with atoms and have received considerable attention. Meanwhile, the analogous nondissipative collective dephasing phenomena mediated by EM environments remain poorly understood. Here, we introduce the nano-EM superdephasing phenomenon arising in the photonic environments near materials. We show that collective dephasing in this nano-EM environment is enhanced by over 10 orders of magnitude compared to free space or cavities. This giant enhancement originates from long-range correlations in off-resonant, low-frequency evanescent EM fluctuations, which lead to collectively accelerated (super) or suppressed (sub) dephasing in many-body entangled states. We further unravel that nano-EM collective dephasing exhibits universal interaction ranges near materials with different anisotropies that can be reciprocal or nonreciprocal. This nano-EM interaction range, which is not present in free space and cavities, leads to unique scaling laws of superdephasing in Greenberger-Horne-Zeilinger states different from the conventional N2 scaling of superradiance. Finally, we discuss how to experimentally isolate and control superdephasing to open interesting frontiers for scalable quantum systems.
Nitrogen-vacancy centers in diamond allow coherent spin state manipulation and optical readout at room temperature, which has powerful applications in nanoscale sensing. Nanophotonic structures such as plasmonic waveguides, nanoantennae, metamaterials, and metasurfaces can enhance the detected fluorescence rate from such broadband emitters. The fluorescence of the coupled emitter is directed into confined plasmonic modes with high photonic density of states. However, an accurate spin readout requires both high photon counts and a strong contrast between the spin states, both of which can be influenced by the Purcell effect. We introduce a novel method for measuring the spin contrast in large nitrogen-vacancy ensembles. We use this method to study how the photonic density of states must be engineered in order to minimize the uncertainty of spin readout in dense NV ensembles. We describe these results using a kinetic model of the nitrogen-vacancy’s internal dynamics.
The holy grail for quantum engineers and scientists is to build the quantum internet that spans over the entire globe. This information infrastructure holds the promise for transmitting information securely, scaling up computing power exponentially and setting the standards for precision measurement at the ultimate limit. Solid-state-based spin systems recently emerge as promising building blocks for the quantum internet. Among these candidates, the negatively charged nitrogen vacancy (NV) center in diamond attracted much attention thanks to its optical addressability, long spin coherence times, and well-controlled electronic orbitals and spin states. However, the non-ideal optical properties of NV poses a challenge to its implementation in quantum technologies. This calls for building photonic structures as efficient spin-photon interfaces for realizing strong interactions with photon modes or efficient out-coupling of its fluorescence. Such interfacing structures are also of great importance for other optically active spin-systems newly found. In this dissertation, chirped dielectric cavities are designed for building NV as fast single photon sources via broadband Purcell enhancement, using an inverse simulation approach to maximize the broadband absorption of the atomically thin absorbers. Simulated NV-cavity coupling indicates broadband Purcell factor of ∼> 100. Next, to realize coupled NV-cavity systems over large scale, a self-aligned nano-implantation technique is investigated using a lithographically defined hybrid mask for both precision pattern transfer and nitrogen implantation. Measured results show single-NV per cavity yield of ∼ 26±1% and 5-fold Purcell induced intensity enhancement. Finally, chirped circular gratings are designed for efficient collection from the NV for remote entanglement and precision sensing. Simulated grating structures present near-unity collection efficiencies. These demonstrated techniques and structures are also applicable to other solid-state-based spin systems.
Electromagnetic (EM) fields can be engineered through controlled modulation of amplitude, phase, frequency, polarization, and angular momentum. Such engineered fields have enabled a wide range of promising applications in modern photonics, nanoscience, and quantum technologies. In the far-field regime, tailoring the spin and orbital angular momentum of light gives rise to structured optical fields with nontrivial topological properties, such as skyrmionic and vortex-like textures. These optical topologies have attracted considerable interest for applications in noise-resilient optical communications, super-resolution imaging, and advanced light-matter interactions. In contrast, near-field EM environments emerge from microscopic spin and charge dynamics within materials. By controlling material composition, dimensionality, and nanoscale structure, it becomes possible to engineer EM fluctuations. Probing the properties of engineered EM fields remains challenging because many of their features, including the nanoscale localization of topological features and the weak, broadband nature of near-field fluctuations, are difficult to access using conventional measurement techniques. This dissertation focuses on quantum probing of engineered EM fields using the nitrogen vacancy (NV) center in diamond, a versatile quantum sensing platform. Both far-field optical topologies and near-field EM fluctuations are investigated, demonstrating how quantum probes can be used to characterize novel EM phenomena across distinct spatial and spectral regimes.In this dissertation, the topological properties of optical beams are probed through the coherent interaction between the photonic spin texture (PST) of structured light and NV center spin qubits. The spatial distribution of photonic spin gives rise to distinct topological features of light. Through local coherent coupling with the NV spin qubit, the PST induces a measurable phase shift in the quantum superposition state of the NV center. By optically measuring the accumulated phase shift of the NV center spin qubits, the local spin texture is quantitatively reconstructed and the topological properties of the optical field are characterized. Through a coherent light-matter interaction, this work also introduces the concept of transducing topological features of light onto the phase texture of NV spin ensemble.To probe the near-field EM fluctuations, the phase coherence decay of NV center spin qubits is measured. Fluctuations arising from spin and charge dynamics within nearby materials induce random phase accumulation in the superposition state of the NV center, leading to dephasing of the spin qubit. Through frequency-selective and spectrally resolved measurements of the NV spin coherence decay rates, the local near-field EM environment is quantitatively characterized. The measured fluctuations are further connected to important materials properties and phenomena, including magnetic dynamics, superparamagnetism, and critical fluctuations in magnetic material and metastructures. Through quantum dephasing measurements, this work reveals previously unexplored material properties and near-field EM phenomena.
Engineering the local density of states with nanophotonic structures is a powerful tool to control light-matter interactions via the Purcell effect. At optical frequencies, control over the electric field density of states is typically used to couple to and manipulate electric dipole transitions. However, it is also possible to engineer the magnetic density of states to control magnetic dipole transitions. In this work, we experimentally demonstrate the optical magnetic Purcell effect using a single rare earth ion coupled to a nanophotonic cavity. We engineer a new single photon emitter, Er3+ in MgO, where the electric dipole decay rate is strongly suppressed by the cubic site symmetry, giving rise to a nearly pure magnetic dipole optical transition. This allows the unambiguous determination of a magnetic Purcell factor Pm=1040±30. We further extend this technique to realize a magnetic dipole spin-photon interface, performing optical spin initialization and readout of a single Er3+ electron spin. This work demonstrates the fundamental equivalence of electric and magnetic density of states engineering, and provides a new tool for controlling light-matter interactions for a broader class of emitters.