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Ultrafast photon echo spectroscopy of luminescent centers: NV:diamond and thulium(3+) yttrium aluminum oxygen(3).

Alan Lenef

Published Jan 1, 1993• 0 citations
OpenAlex

Abstract

In the present work, ultrafast photon echo spectroscopy has been applied to investigate dephasing dynamics and excited state electronic structure of impurity N-V centers in diamond and Tm$\sp{3+}$-Tm$\sp{3+}$ centers. In the N-V center, quantum beat measurements revealed modulation frequencies of 0.63 $\pm$ 0.02 GHz, 1.650 $\pm$ 0.003 GHz, and 2.298 $\pm$ 0.006 GHz which furnished excited state spin-spin splittings directly for the first time. Wavelength dependent studies of dephasing times showed conclusively the existence of a larger splitting of 46 $\pm$ 2 cm$\sp{-1}$ in the excited E state. These results were found to be consistent with temperature dependent studies which reveal dephasing, near liquid-He temperatures, is dominated by a one-phonon direct dephasing process in the upper state with an activation energy of 68 $\pm$ 16 cm$\sp{-1}$ has a two-phonon Orbach contribution to dephasing in the lower state with an activation energy of 39 $\pm$ 5 cm$\sp{-1}.$ Experiments with circularly polarized light also revealed an interesting polarization selection rule originating from Zeeman coherence in the doublet E spin state of the $\sp3A$ ground state. A complete multi-electron model is presented which makes use of a previously undetected Jahn-Teller effect to explain all the observed excited state structure. An extension of these ultrafast techniques were applied to Tm$\sp{3+}$-Tm$\sp{3+}$ centers in YAlO$\sb3,$ permitting the first preliminary investigations of coherent dynamics on highly cooperative transitions. Dephasing times on the $\sp3F\sb4(\Gamma\sp2)$ $\to$ $\sp1G\sb4(\Gamma\sp1)$ excited state transitions were found to increase from 35 $\pm$ 2 ps to 61 $\pm$ 6 ps with decreasing intensity of a resonant auxiliary cw laser which populates this transition in a controllable fashion. Temperature dependence studies revealed dephasing on this cooperative transition was dominated by a direct process with an activation energy of 157 $\pm$ 16 cm$\sp{-1}$ at liquid-He temperatures. These results were consistent with expected dephasing rate dependence for interacting Tm$\sp{3+}$-Tm$\sp{3+}$ centers.

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Electronic structure of the N-Vcenter in diamond: Experiments

Alan Lenef, Steven W. Brown, David A. Redman +3 more

Quantum-beat spectroscopy has been used to observe excited states of the N-V center in diamond. For the 1.945-eV optical transition, direct evidence is presented for the existence of GHz-scale fine structure, together with a much larger 46-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ level splitting in the E state. An interference effect observed in transient four-wave-mixing response is explained with a polarization selection rule involving Zeeman coherence among magnetic sublevels. Also, detailed dephasing measurements versus temperature and wavelength have identified the decay mechanisms operative among the various states. A comparison of these results with ab initio calculations of excited electronic structure and interactions based on several multielectron models supports the conclusion that the N-V center is a neutral, two-electron center governed by a strong Jahn-Teller effect and weak spin-spin interactions. \textcopyright{} 1996 The American Physical Society.

Physical review. B, Condensed matter•May 15, 1996•68 citations

Jahn-Teller-induced femtosecond electronic depolarization dynamics of the nitrogen-vacancy defect in diamond

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Abstract Single-photon emission from the nitrogen-vacancy defect in diamond constitutes one of its many proposed applications. Owing to its doubly degenerate 3E electronic excited state, photons from this defect can be emitted by two optical transitions with perpendicular polarization. Previous measurements have indicated that orbital-selective photoexcitation does not, however, yield photoluminescence with well-defined polarizations, thus hinting at orbital-averaging dynamics even at cryogenic temperatures. Here we employ femtosecond polarization anisotropy spectroscopy to investigate the ultrafast electronic dynamics of the 3E state. We observe subpicosecond electronic dephasing dynamics even at cryogenic temperatures, up to five orders of magnitude faster than dephasing rates suggested by previous frequency- and time-domain measurements. Ab initio molecular dynamics simulations assign the ultrafast depolarization dynamics to nonadiabatic transitions and phonon-induced electronic dephasing between the two components of the 3E state. Our results provide an explanation for the ultrafast orbital averaging that exists even at cryogenic temperatures.

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Abstract Many applications of nitrogen-vacancy (NV) centers in diamond crucially rely on a spectrally narrow and stable optical zero-phonon line transition. Though many impressive proof-of-principle experiments have been demonstrated, much work remains in engineering NV centers with spectral properties that are sufficiently robust for practical implementation. To elucidate the mechanisms underlying their interactions with the environment, we apply multi-dimensional coherent spectroscopy to an NV center ensemble in bulk diamond at cryogenic temperatures. Our spectra reveal thermal dephasing due to quasi-localized vibrational modes as well as ultrafast spectral diffusion on the picosecond timescale. The intrinsic, ensemble-averaged homogeneous linewidth is found to be in the tens of GHz range by extrapolating to zero temperature. We also observe a temperature-dependent Stark splitting of the excited state manifold, relevant to NV sensing protocols.

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The phonon-modulated Jahn–Teller distortion of the nitrogen vacancy center in diamond

William P. Carbery, Camille A. Farfan, Ronald Ulbricht +1 more

The negatively charged nitrogen vacancy (NV) center in diamond is an optically accessible material defect with a unique combination of spin and optical properties that has attracted interest in quantum-information sciences and as a design candidate for nanoscale quantum sensors. Here, we present time-resolved nonlinear optical spectroscopy measurements, conducted with ultrabroadband laser pulses, that reveal strong modulation of the excited-state by the longitudinal optical (LO) phonon of the diamond lattice. The LO phonon and its overtones geometrically distort neighboring NV centers, driving long lived (3.5 ps) excited state relaxation of coupled NV centers after the initial excitation and ultrafast (<150 fs) decay of the Jahn-Teller distortion. These observations elevate the LO phonon to an important tuning mode of the Jahn-Teller conical intersection and help resolve previous spectroscopy experiments that noted longer-lived excited-state dynamics.

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Electronic structure of the nitrogen-vacancy color center in diamond.

David A. Redman

The nitrogen - vacancy (N-V) center is a point defect found in diamonds containing substitutional nitrogen impurities. It arises after exposure to ionizing radiation and subsequent thermal annealing. The physical structure of the center has previously been identified as a substitutional nitrogen atom located adjacent to a neutral carbon vacancy, but prior to this work knowledge of its electronic structure was very incomplete. The results presented here are intended to establish the energy level structure of the N-V center unambiguously, using nonlinear laser spectroscopy in concert with paramagnetic resonance experiments. A new technique which achieves sub-Hertz resolution in nearly degenerate four-wave mixing (NDFWM) and optical two-beam coupling experiments was applied to determine the decay rates of excited states in the N-V center. Laser-enhanced EPR experiments were performed to assign spin character to the ground state. Fluorescent emission of the center was used to determine excited state energies. In particular, these results resolve earlier conflicting reports of the N-V ground state structure and offer a picture of state energies and dynamics consistent with all observations to date. The principal results of this thesis may be summarized as follows. We show that the ground state of the center consists of a spin triplet ground state with a zero-field splitting of 2.88 GHz and a spin-lattice relaxation time of 1.170 $\pm$ 0.003 ms. The first parity-allowed transition occurs to a triplet excited state at 1.944 eV with a lifetime of 13.3 $\pm$ 0.2 ns. The first metastable singlet excited state is shown to have a lifetime of 265.3 $\pm$ 0.6 ms at room temperature and its temperature dependence measured between 77 and 295 K. Through low temperature studies the mechanism for ground state spin-lattice relaxation is determined to be a two-phonon process involving 63 meV optical phonons. Finally, the origin of satellite lines in the persistent hole-burning spectrum is tentatively explained using our picture of the energy level structure and used to infer a zero-field spin splitting in the excited triplet state of 0.6 GHz.

•Jan 1, 1991•0 citations

Manipulation and measurement of quantum states of single spins

Jörg Wrachtrup

Defects determine the mechanical, electrical and optical properties in solids. Often their chemical nature is very simple, comprising for example just a simple lattice vacancy or a single atom impurity. Some defects are optically active, i.e. they show allowed optical transitions. Those defect are called colour centers and often determine the optical properties of the respective solid. Famous examples are colour centers in ruby or alkali halides. By careful control of defect center concentration in combination with optical microscopy it became recently possible to investigate single defect centers optically. One of the materials that was investigated in particular detail is diamond. Pure diamond is an optically transparent medium. However more than 100 colour centers have been identified in diamond. Owing to its energy level structure the nitrogen vacancy center in diamond is a particularly interesting one to investigate. This defect center has a paramagnetic ground and first excited state. The resulting fine structure splitting can be resolved by low temperature fluorescence excitation spectroscopy. Ground as well as first excited state are spin triplets, i.e. S=1. When spin angular momentum is conserved during optical excitation one thus expects to find three optical excitation lines owing to the three spin sub levels in each electronic state. Indeed conservation of spin angular momentum during excitation seems to be fulfilled, however only a single excitation line is found. Experimentally this is due to unfavourable photophysical properties of the other transitions. Because of low electron phonon coupling of the center the linewidth of the transition is limited by the lifetime of the optically excited state and not, as in most cases, by dephasing due to electron-phonon coupling. Due to this low electron-phonon coupling all of the oscillator strength of the optical transition is concentrated in a narrow frequency interval giving rise to a large on resonance absorption cross section. This large cross section allows for ms averaging times, which are much smaller than the spin lattice relaxation times. One thus is able to determine the specific electron spin state the defect center is in. In diamonds isotopically enriched with 13C, the electron spin of the defect center is coupled to the nuclear spins of the surrounding 13C nuclei by hyperfine interaction. The hyperfine coupling depends on the distance of the center of the defect to the nuclei. For nuclei in the first coordination shell around the defect the coupling strength is around 250 MHz for nuclei in the second shell it is roughly 60 MHz. The hyperfine coupling is thus resolvable in single defect center excitation spectra. The spin relaxation times of nuclei in diamond are even longer than those of the electron. One thus is also able to determine the nuclear spin states around the defect center. Simultaneous radiation with radio frequency generates magnetic dipole transition and thus allows to control the nuclear spin states around the center. The system provides an interesting example for readout and manipulation of single spin degrees of freedom which may be interesting as hardware in future quantum information processing application.

Conference on Lasers and Electro-Optics•Jan 1, 2004•0 citations
In the present work, ultrafast photon echo spectroscopy has been applied to investigate dephasing dynamics and excited state electronic structure of impurity N-V centers in diamond and Tm\sp3+\sp{3+}\sp3+-Tm\sp3+\sp{3+}\sp3+ centers. In the N-V center, quantum beat measurements revealed modulation frequencies of 0.63 ±\pm± 0.02 GHz, 1.650 ±\pm± 0.003 GHz, and 2.298 ±\pm± 0.006 GHz which furnished excited state spin-spin splittings directly for the first time. Wavelength dependent studies of dephasing times showed conclusively the existence of a larger splitting of 46 ±\pm± 2 cm\sp−1\sp{-1}\sp−1 in the excited E state. These results were found to be consistent with temperature dependent studies which reveal dephasing, near liquid-He temperatures, is dominated by a one-phonon direct dephasing process in the upper state with an activation energy of 68 ±\pm± 16 cm\sp−1\sp{-1}\sp−1 has a two-phonon Orbach contribution to dephasing in the lower state with an activation energy of 39 ±\pm± 5 cm\sp−1.\sp{-1}.\sp−1. Experiments with circularly polarized light also revealed an interesting polarization selection rule originating from Zeeman coherence in the doublet E spin state of the \sp3A\sp3A\sp3A ground state. A complete multi-electron model is presented which makes use of a previously undetected Jahn-Teller effect to explain all the observed excited state structure. An extension of these ultrafast techniques were applied to Tm\sp3+\sp{3+}\sp3+-Tm\sp3+\sp{3+}\sp3+ centers in YAlO\sb3,\sb3,\sb3, permitting the first preliminary investigations of coherent dynamics on highly cooperative transitions. Dephasing times on the \sp3F\sb4(Γ\sp2)\sp3F\sb4(\Gamma\sp2)\sp3F\sb4(Γ\sp2) →\to→ \sp1G\sb4(Γ\sp1)\sp1G\sb4(\Gamma\sp1)\sp1G\sb4(Γ\sp1) excited state transitions were found to increase from 35 ±\pm± 2 ps to 61 ±\pm± 6 ps with decreasing intensity of a resonant auxiliary cw laser which populates this transition in a controllable fashion. Temperature dependence studies revealed dephasing on this cooperative transition was dominated by a direct process with an activation energy of 157 ±\pm± 16 cm\sp−1\sp{-1}\sp−1 at liquid-He temperatures. These results were consistent with expected dephasing rate dependence for interacting Tm\sp3+\sp{3+}\sp3+-Tm\sp3+\sp{3+}\sp3+ centers.
Quantum-beat spectroscopy has been used to observe excited states of the N-V center in diamond. For the 1.945-eV optical transition, direct evidence is presented for the existence of GHz-scale fine structure, together with a much larger 46-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ level splitting in the E state. An interference effect observed in transient four-wave-mixing response is explained with a polarization selection rule involving Zeeman coherence among magnetic sublevels. Also, detailed dephasing measurements versus temperature and wavelength have identified the decay mechanisms operative among the various states. A comparison of these results with ab initio calculations of excited electronic structure and interactions based on several multielectron models supports the conclusion that the N-V center is a neutral, two-electron center governed by a strong Jahn-Teller effect and weak spin-spin interactions. \textcopyright{} 1996 The American Physical Society.
Abstract Single-photon emission from the nitrogen-vacancy defect in diamond constitutes one of its many proposed applications. Owing to its doubly degenerate 3E electronic excited state, photons from this defect can be emitted by two optical transitions with perpendicular polarization. Previous measurements have indicated that orbital-selective photoexcitation does not, however, yield photoluminescence with well-defined polarizations, thus hinting at orbital-averaging dynamics even at cryogenic temperatures. Here we employ femtosecond polarization anisotropy spectroscopy to investigate the ultrafast electronic dynamics of the 3E state. We observe subpicosecond electronic dephasing dynamics even at cryogenic temperatures, up to five orders of magnitude faster than dephasing rates suggested by previous frequency- and time-domain measurements. Ab initio molecular dynamics simulations assign the ultrafast depolarization dynamics to nonadiabatic transitions and phonon-induced electronic dephasing between the two components of the 3E state. Our results provide an explanation for the ultrafast orbital averaging that exists even at cryogenic temperatures.
Abstract Many applications of nitrogen-vacancy (NV) centers in diamond crucially rely on a spectrally narrow and stable optical zero-phonon line transition. Though many impressive proof-of-principle experiments have been demonstrated, much work remains in engineering NV centers with spectral properties that are sufficiently robust for practical implementation. To elucidate the mechanisms underlying their interactions with the environment, we apply multi-dimensional coherent spectroscopy to an NV center ensemble in bulk diamond at cryogenic temperatures. Our spectra reveal thermal dephasing due to quasi-localized vibrational modes as well as ultrafast spectral diffusion on the picosecond timescale. The intrinsic, ensemble-averaged homogeneous linewidth is found to be in the tens of GHz range by extrapolating to zero temperature. We also observe a temperature-dependent Stark splitting of the excited state manifold, relevant to NV sensing protocols.
The negatively charged nitrogen vacancy (NV) center in diamond is an optically accessible material defect with a unique combination of spin and optical properties that has attracted interest in quantum-information sciences and as a design candidate for nanoscale quantum sensors. Here, we present time-resolved nonlinear optical spectroscopy measurements, conducted with ultrabroadband laser pulses, that reveal strong modulation of the excited-state by the longitudinal optical (LO) phonon of the diamond lattice. The LO phonon and its overtones geometrically distort neighboring NV centers, driving long lived (3.5 ps) excited state relaxation of coupled NV centers after the initial excitation and ultrafast (<150 fs) decay of the Jahn-Teller distortion. These observations elevate the LO phonon to an important tuning mode of the Jahn-Teller conical intersection and help resolve previous spectroscopy experiments that noted longer-lived excited-state dynamics.
The nitrogen - vacancy (N-V) center is a point defect found in diamonds containing substitutional nitrogen impurities. It arises after exposure to ionizing radiation and subsequent thermal annealing. The physical structure of the center has previously been identified as a substitutional nitrogen atom located adjacent to a neutral carbon vacancy, but prior to this work knowledge of its electronic structure was very incomplete. The results presented here are intended to establish the energy level structure of the N-V center unambiguously, using nonlinear laser spectroscopy in concert with paramagnetic resonance experiments. A new technique which achieves sub-Hertz resolution in nearly degenerate four-wave mixing (NDFWM) and optical two-beam coupling experiments was applied to determine the decay rates of excited states in the N-V center. Laser-enhanced EPR experiments were performed to assign spin character to the ground state. Fluorescent emission of the center was used to determine excited state energies. In particular, these results resolve earlier conflicting reports of the N-V ground state structure and offer a picture of state energies and dynamics consistent with all observations to date. The principal results of this thesis may be summarized as follows. We show that the ground state of the center consists of a spin triplet ground state with a zero-field splitting of 2.88 GHz and a spin-lattice relaxation time of 1.170 ±\pm± 0.003 ms. The first parity-allowed transition occurs to a triplet excited state at 1.944 eV with a lifetime of 13.3 ±\pm± 0.2 ns. The first metastable singlet excited state is shown to have a lifetime of 265.3 ±\pm± 0.6 ms at room temperature and its temperature dependence measured between 77 and 295 K. Through low temperature studies the mechanism for ground state spin-lattice relaxation is determined to be a two-phonon process involving 63 meV optical phonons. Finally, the origin of satellite lines in the persistent hole-burning spectrum is tentatively explained using our picture of the energy level structure and used to infer a zero-field spin splitting in the excited triplet state of 0.6 GHz.
Defects determine the mechanical, electrical and optical properties in solids. Often their chemical nature is very simple, comprising for example just a simple lattice vacancy or a single atom impurity. Some defects are optically active, i.e. they show allowed optical transitions. Those defect are called colour centers and often determine the optical properties of the respective solid. Famous examples are colour centers in ruby or alkali halides. By careful control of defect center concentration in combination with optical microscopy it became recently possible to investigate single defect centers optically. One of the materials that was investigated in particular detail is diamond. Pure diamond is an optically transparent medium. However more than 100 colour centers have been identified in diamond. Owing to its energy level structure the nitrogen vacancy center in diamond is a particularly interesting one to investigate. This defect center has a paramagnetic ground and first excited state. The resulting fine structure splitting can be resolved by low temperature fluorescence excitation spectroscopy. Ground as well as first excited state are spin triplets, i.e. S=1. When spin angular momentum is conserved during optical excitation one thus expects to find three optical excitation lines owing to the three spin sub levels in each electronic state. Indeed conservation of spin angular momentum during excitation seems to be fulfilled, however only a single excitation line is found. Experimentally this is due to unfavourable photophysical properties of the other transitions. Because of low electron phonon coupling of the center the linewidth of the transition is limited by the lifetime of the optically excited state and not, as in most cases, by dephasing due to electron-phonon coupling. Due to this low electron-phonon coupling all of the oscillator strength of the optical transition is concentrated in a narrow frequency interval giving rise to a large on resonance absorption cross section. This large cross section allows for ms averaging times, which are much smaller than the spin lattice relaxation times. One thus is able to determine the specific electron spin state the defect center is in. In diamonds isotopically enriched with 13C, the electron spin of the defect center is coupled to the nuclear spins of the surrounding 13C nuclei by hyperfine interaction. The hyperfine coupling depends on the distance of the center of the defect to the nuclei. For nuclei in the first coordination shell around the defect the coupling strength is around 250 MHz for nuclei in the second shell it is roughly 60 MHz. The hyperfine coupling is thus resolvable in single defect center excitation spectra. The spin relaxation times of nuclei in diamond are even longer than those of the electron. One thus is also able to determine the nuclear spin states around the defect center. Simultaneous radiation with radio frequency generates magnetic dipole transition and thus allows to control the nuclear spin states around the center. The system provides an interesting example for readout and manipulation of single spin degrees of freedom which may be interesting as hardware in future quantum information processing application.