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Characterizing the Nonlinear Optical Response of Silicon Vacancy Centers in Diamond and Showcasing the Next Generation of Optical Frequency Combs

Matthew Day

Published Jan 1, 2021• 0 citations
Publisher

Abstract

In the first half of this work, we employ multidimensional coherent spectroscopy (MDCS) to show that a previously unknown hidden population of dark silicon-vacancy centers dominates the resonant nonlinear optical response of an ensemble of such centers. We present evidence to support our assertion that this phenomenon is due to strain-induced coupling to a dark state. We posit two mechanisms by which this could occur. Furthermore, we use a particular version of MDCS sensitive only to excitation dependent interactions between color centers, known as double-quantum spectroscopy, to show that inter-center interactions (causing peak shifts on the order of between 4 and 40 GHz) occur in our sample and are likely electronic dipole-dipole interactions. We demonstrate rudimentary control over the interaction strength between color center pairs by introducing an intense optical pulse and varying the pulse strength. As a function of the pulse field, the double quantum spectra show pairwise Rabi-like oscillations in the peak amplitude, which is a direct signature of varying interaction strength. In the latter half of this thesis, we showcase a new breed of semiconductor diode-based miniaturized frequency combs. Two dozen of our combs fit within a grain of rice. In this thesis, we characterize the modelocking physics of these frequency combs. We show that these lasers output coherent frequency modulated frequency combs, providing evidence that passive modelocking within the laser cavity occurs to stabilize the comb output. Beyond demonstrating that these frequency combs are indeed coherent, we also demonstrate their use in a practical dual-comb spectroscopy application. We acquire a dual-comb absorption spectrum of a gas cell, with a resolution better than 25 GHz achieved in only 10 µs of data acquisition time. We also show that these frequency combs can be battery powered, and that they are efficient, tunable, and simple. This thesis shows that diode frequency combs are truly portable and capable of providing a platform for practical precision measurement to thrive.

DOI
10.7302/3095

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We report tunable excitation-induced dipole-dipole interactions between silicon-vacancy color centers in diamond at cryogenic temperatures. These interactions couple centers into collective states, and excitation-induced shifts tag the excitation level of these collective states against the background of excited single centers. By characterizing the phase and amplitude of the spectrally resolved interaction-induced signal, we observe oscillations in the interaction strength and population state of the collective states as a function of excitation pulse area. Our results demonstrate that excitation-induced dipole-dipole interactions between color centers provide a route to manipulating collective intercenter states in the context of a congested, inhomogeneous ensemble.

arXiv:2105.01103•Physical Review Letters•May 17, 2022•16 citations
In the first half of this work, we employ multidimensional coherent spectroscopy (MDCS) to show that a previously unknown hidden population of dark silicon-vacancy centers dominates the resonant nonlinear optical response of an ensemble of such centers. We present evidence to support our assertion that this phenomenon is due to strain-induced coupling to a dark state. We posit two mechanisms by which this could occur. Furthermore, we use a particular version of MDCS sensitive only to excitation dependent interactions between color centers, known as double-quantum spectroscopy, to show that inter-center interactions (causing peak shifts on the order of between 4 and 40 GHz) occur in our sample and are likely electronic dipole-dipole interactions. We demonstrate rudimentary control over the interaction strength between color center pairs by introducing an intense optical pulse and varying the pulse strength. As a function of the pulse field, the double quantum spectra show pairwise Rabi-like oscillations in the peak amplitude, which is a direct signature of varying interaction strength. In the latter half of this thesis, we showcase a new breed of semiconductor diode-based miniaturized frequency combs. Two dozen of our combs fit within a grain of rice. In this thesis, we characterize the modelocking physics of these frequency combs. We show that these lasers output coherent frequency modulated frequency combs, providing evidence that passive modelocking within the laser cavity occurs to stabilize the comb output. Beyond demonstrating that these frequency combs are indeed coherent, we also demonstrate their use in a practical dual-comb spectroscopy application. We acquire a dual-comb absorption spectrum of a gas cell, with a resolution better than 25 GHz achieved in only 10 µs of data acquisition time. We also show that these frequency combs can be battery powered, and that they are efficient, tunable, and simple. This thesis shows that diode frequency combs are truly portable and capable of providing a platform for practical precision measurement to thrive.
This work covers two main results united by multidimensional coherent spectroscopy (MDCS): one experimental and one theoretical. MDCS is a nonlinear optical technique in which a sample is probed using a series of ultrashort pulses. Measurements are made while varying the relative time delays between the pulses, and the resulting spectra yield a much richer set of information compared to traditional linear spectroscopies. The experimental work concerns the negatively charged silicon-vacancy (SiV) center in diamond. We use two-pulse correlation (TPC) spectroscopy and rephasing MDCS to probe a diamond sample with a high density of implanted SiV centers. These spectra reveal a large number of spectral peaks, which can be grouped into two families of SiV centers using the MDCS spectra. By comparing spectra from two polarizations of the incident light, we associate the two families with two orientation groups within the diamond. We link the differences in the frequencies of the spectral peaks to strain intrinsic to our sample, and use the peak locations from both families to solve for the full strain tensor local to the laser spot. By measuring TPC spectra at multiple points on the sample, we track changes in the measured strain. We observe non-zero strain on the order or 1e-5 at every measured location, and observe variation in both the normal and shear strain in the sample. We interpret the strain as likely to be due to the high implantation density of silicon in the diamond. These results could be useful when using SiV centers as a strain gauge. The theoretical work uses simulations to calculate spectra. The simulations developed here begin by recursively generating a list of Feynman diagrams for a given signal pathway and system. The contributions due to each Feynman diagram are calculated and combined to find the complete spectrum. The code is designed to be very flexible, and can be used to simulate arbitrary types of MDCS spectra and energy level diagrams. We then apply the simulations to investigate the effects of correlated dephasing due to scattering events in the Markovian limit on MDCS of interacting systems. We derive a mathematical expression to represent the dephasing rate of a coherence in terms of the dephasing rates of the coherences from the constituent energy transitions and the correlation matrix of these transitions. This expression is applied to simulate double-quantum and higher-order n-quantum spectra of multiple interacting systems. For double-quantum spectra, correlated dephasing results in a higher double-quantum dephasing rate, and anticorrelated dephasing results in a lower double-quantum dephasing rate. Similar results are found for the n-quantum dephasing rate. Generally, for certain configurations, the many-body dephasing rate can be arbitrarily low, and the n-quantum linewidth can be arbitrarily narrow, although this requires some form of anticorrelation. These results could be useful in creating quantum sensors with higher sensitivities, since one limit of the sensitivity is the decoherence time of the system.
Color centers in diamond are point defects within the diamond host lattice that absorb and emit light at optical frequencies. Besides contributing to the striking visual characteristics of "fancy colored" diamonds as gemstones, the centers--particularly the negatively charged nitrogen-vacancy (NV) center and silicon-vacancy (SiV-) center--offer a number of possibilities for quantum computation and quantum information processing. In this talk, I will summarize recent progress made in characterizing negatively charged silicon-vacancy centers in diamond using the technique of optical multidimensional coherent spectroscopy (MDCS). By comparing photoluminescence-based and heterodyne-detection based signal collection schemes in a high-density SiV- center sample, we have selectively identified a population of long-lived and nonradiative silicon-vacancy centers in diamond with more than 40 times as much inhomogeneous spectral broadening as the radiative silicon-vacancy center states that are more commonly observed using photoluminescence. Estimates of the degree of inhomogeneity and overall sample characteristics indicate that strain is likely to play a large role in the formation of these nonradiative states. The findings open possibilities for being able to actively tune the degree of radiative coupling in silicon-vacancy center systems, opening possibilities for new types of quantum-optical devices.
Negatively charged silicon-vacancy (SiV−^-−) centers in diamond offer an attractive platform for the development of many forms of quantum technology. However, questions remain in connection to how large ensembles of SiV−^-− centers behave in concert. Here, we develop a computational model designed to simulate recent experiments where optical multidimensional coherent spectroscopy (MDCS) was used to examine a high-concentration sample of SiV−^-− centers in diamond, revealing significant variations in spectral signature depending on the detection scheme. Simulation results reveal that strain effects are highly random in this system, with a characteristic axial strain of 2.8×10−42.8 \times 10^{-4}2.8×10−4 and a shear strain of 3.5×10−53.5 \times 10^{-5}3.5×10−5. They suggest in addition that highly strained centers (with values exceeding 1.5×10−51.5 \times 10^{-5}1.5×10−5) may become significantly decoupled from optical emission. The results have implications for the use of SiV−^-− centers as quantum sensors.
We characterize a high-density sample of negatively charged silicon-vacancy (SiV^{-}) centers in diamond using collinear optical multidimensional coherent spectroscopy. By comparing the results of complementary signal detection schemes, we identify a hidden population of SiV^{-} centers that is not typically observed in photoluminescence and which exhibits significant spectral inhomogeneity and extended electronic T_{2} times. The phenomenon is likely caused by strain, indicating a potential mechanism for controlling electric coherence in color-center-based quantum devices.
Quantum optomechanical technologies benefit from mechanical oscillators that are high-frequency, can be coherently driven, and are capable of coupling to other quantum systems. Diamond supports all of these criteria: its large elastic modulus increases mechanical resonance frequency, its low nonlinear optical absorption increases the allowed intensity of fields used for coherent optomechanics, and it hosts spin qubits that interact with mechanical modes. Here we demonstrate a diamond optomechanical crystal cavity that supports multiple mechanical resonances with $\sim$12 GHz frequency and high Qm×fmQ_\text{m} \times f_\text{m}Qm​×fm​ product that can be coherently coupled to multiple optical modes. By exciting this sideband resolved system into mechanical self-sustained oscillations, we generate a frequency comb spanning 143 GHz. Analysis of the comb spectrum, combined with systematic characterization of the system's optomechanical coupling, allows us to quantitatively show that its mechanical oscillation amplitude reaches 130 pm. This corresponds to a maximum total dynamic strain of 1.1×10−31.1 \times 10^{-3}1.1×10−3 that is sufficiently high for future demonstrations of optomechanical control of diamond spin qubits.
We report tunable excitation-induced dipole-dipole interactions between silicon-vacancy color centers in diamond at cryogenic temperatures. These interactions couple centers into collective states, and excitation-induced shifts tag the excitation level of these collective states against the background of excited single centers. By characterizing the phase and amplitude of the spectrally resolved interaction-induced signal, we observe oscillations in the interaction strength and population state of the collective states as a function of excitation pulse area. Our results demonstrate that excitation-induced dipole-dipole interactions between color centers provide a route to manipulating collective intercenter states in the context of a congested, inhomogeneous ensemble.