Coherence Lifetime Research Articles

Towards implementation of a magic optical-dipole trap for confining ground-state and Rydberg-state cesium cold atoms

Long ground-Rydberg coherence lifetime is interesting for implementing high-fidelity quantum logic gates, many-body physics, and other quantum information protocols. However, the potential formed by a conventional far-off-resonance red-detuned optical-dipole trap (ODT) is usually repulsive for Rydberg atoms, which will result in fast atom loss and low repetition rate of the experimental sequence. These issues can be addressed by a magic ODT. We performed the calculation of ODT’s magic detuning for confinement of ground-state and Rydberg-state cesium atoms with the same potential well. We used a sum-over-states method to calculate the dynamic polarizabilities of 6S1/2 ground state and highly-excited (nS1/2 and nP3/2) Rydberg state of cesium atoms, and identify corresponding magic detuning for optical wavelengths in the range of 850–1950 nm. We estimated the trapping lifetime of cesium Rydberg atoms confined in the magic ODT by including different dissipative mechanisms. Furthermore, we have experimentally realized an 1879.43 nm single-frequency laser system with a watt-level output power for setting up the magic ODT for 6S1/2 ground-state and 84P3/2 Rydberg-state cesium cold atoms.

Room Temperature Terahertz Electroabsorption Modulation by Excitons in Monolayer Transition Metal Dichalcogenides.

The interaction between off-resonant laser pulses and excitons in monolayer transition metal dichalcogenides is attracting increasing interest as a route for the valley-selective coherent control of the exciton properties. Here, we extend the classification of the known off-resonant phenomena by unveiling the impact of a strong THz field on the excitonic resonances of monolayer MoS2. We observe that the THz pump pulse causes a selective modification of the coherence lifetime of the excitons, while keeping their oscillator strength and peak energy unchanged. We rationalize these results theoretically by invoking a hitherto unobserved manifestation of the Franz-Keldysh effect on an exciton resonance. As the modulation depth of the optical absorption reaches values as large as 0.05 dB/nm at room temperature, our findings open the way to the use of semiconducting transition metal dichalcogenides as compact and efficient platforms for high-speed electroabsorption devices.

Hyperfine interaction and coherence time of praseodymium ions at the site 2 in yttrium orthosilicate

Praseodymium (Pr3+) ions doped in the site 1 of yttrium orthosilicate (Y2SiO5) has been widely employed as the photonic quantum memory due to their excellent optical coherence and spin coherence. While praseodymium ions occupying the site 2 in Y2SiO5 crystal have better optical coherence as compared with those at site 1, which may enable better performance in quantum memory. Here we experimentally characterize the hyperfine interactions of the ground state 3H4 and excited state 1D2 of Pr3+ at site 2 in Y2SiO5 using Raman heterodyne detected nuclear magnetic resonance. The Hamiltonians for the hyperfine interaction are reconstructed for both ground state 3H4 and excited state 1D2 based on the Raman heterodyne spectra in 201 magnetic fields. The two-pulse spin-echo coherence lifetime for the ground state is measured to be 2.6 ± 0.1 ms at site 2 with zero magnetic field, which is more than five times longer than that at site 1. The magnetic fields with zero first order Zeeman shift in the hyperfine transition for Pr3+ at site 2 in Y2SiO5 are identified.

Attosecond Time-Domain Measurement of Core-Level-Exciton Decay in Magnesium Oxide.

Excitation of ionic solids with extreme ultraviolet pulses creates localized core-level excitons, which in some cases couple strongly to the lattice. Here, core-level-exciton states of magnesium oxide are studied in the time domain at the Mg L_{2,3} edge with attosecond transient reflectivity spectroscopy. Attosecond pulses trigger the excitation of these short-lived quasiparticles, whose decay is perturbed by time-delayed near-infrared pulses. Combined with a few-state theoretical model, this reveals that the infrared pulse shifts the energy of bright (dipole-allowed) core-level-exciton states as well as induces features arising from dark core-level excitons. We report coherence lifetimes for the two lowest core-level excitons of 2.3±0.2 and 1.6±0.5 fs and show that these are primarily a consequence of strong exciton-phonon coupling, disclosing the drastic influence of structural effects in this ultrafast relaxation process.

A calibration method for coil constants using an atomic spin self-sustaining vector magnetometer

The self-sustaining atomic magnetometer has the advantage of high sensitivity and long spin coherence lifetime, based on which we demonstrate a novel method to calibrate the magnetic coil constants precisely. Via non-destructive phase measurement and coherent optical pumping, the spin polarization of rubidium atoms is regenerated coherently and the Larmor precession signal is oscillating continuously. In this stable state, the calibrating capability is achieved by applying current to coils and scan the magnetic components along x- and y-direction. The magnetic field magnitude is obtained from precession frequency and the coil constants can be derived from the fitting equation directly. The constants of coils in the experiment are 246.010 ± 0.034 nT/mA and 197.452 ± 0.025 nT/mA in the x- and y-directions, respectively.

Improving wafer-scale Josephson junction resistance variation in superconducting quantum coherent circuits

Quantum bits, or qubits, are an example of coherent circuits envisioned for next-generation computers and detectors. A robust superconducting qubit with a coherent lifetime of O(100 µs) is the transmon: a Josephson junction functioning as a non-linear inductor shunted with a capacitor to form an anharmonic oscillator. In a complex device with many such transmons, precise control over each qubit frequency is often required, and thus variations of the junction area and tunnel barrier thickness must be sufficiently minimized to achieve optimal performance while avoiding spectral overlap between neighboring circuits. Simply transplanting our recipe optimized for single, stand-alone devices to wafer-scale (producing 64, 1x1 cm dies from a 150 mm wafer) initially resulted in global drifts in room-temperature tunneling resistance of ± 30%. Inferring a critical current variation from this resistance distribution, we present an optimized process developed from a systematic 38 wafer study that results in < 3.5% relative standard deviation (RSD) in critical current () for 3000 Josephson junctions (both single-junctions and asymmetric SQUIDs) across an area of 49 cm2. Looking within a 1x1 cm moving window across the substrate gives an estimate of the variation characteristic of a given qubit chip. Our best process, utilizing ultrasonically assisted development, uniform ashing, and dynamic oxidation has shown = 1.8% within 1x1 cm, on average, with a few 1x1 cm areas having < 1.0% (equivalent to < 0.5%). Such stability would drastically improve the yield of multi-junction chips with strict critical current requirements.

La3+ and Er3+ co-doped Y2O3 transparent ceramics with a tunable refractive index and long coherence lifetime

La3+ is used as an index modifier to tune the refractive index of Er3+ doped Y2O3 transparent ceramics without reducing the coherence lifetime of Er3+ 4I13/2−4I15/2 transition. La3+ and Er3+ are incorporated into Y2O3 through a solution-phase nanoparticle synthesis and nanoparticles are sintered into transparent ceramics by hot isostatic press. The maximum La3+ doping concentration is about 10%, which increases the refractive index of Y2O3 by 0.009 (Δn/n = 0.48%). La3+ doping doesn’t reduce Er3+ optical coherence lifetime. The homogeneous linewidth of Er3+(20 ppm) 4I13/2−4I15/2 transition in La3+ doped Y2O3 ceramics is about 10 kHz at 2 K and 0.65 T, which is close to the reported homogeneous linewidth in Er3+ doped Y2O3 ceramics and single crystals. Such La3+ Er3+ co-doped Y2O3 ceramics are proper materials to fabricate optical waveguides for quantum memory applications.

Electromagnetic 0.1-100 kHz noise does not disrupt orientation in a night-migrating songbird implying a spin coherence lifetime of less than 10 µs.

According to the currently prevailing theory, the magnetic compass sense in night-migrating birds relies on a light-dependent radical-pair-based mechanism. It has been shown that radio waves at megahertz frequencies disrupt magnetic orientation in migratory birds, providing evidence for a quantum-mechanical origin of the magnetic compass. Still, many crucial properties, e.g. the lifetime of the proposed magnetically sensitive radical pair, remain unknown. The current study aims to estimate the spin coherence time of the radical pair, based on the behavioural responses of migratory birds to broadband electromagnetic fields covering the frequency band 0.1-100 kHz. A finding that the birds were unable to use their magnetic compass under these conditions would imply surprisingly long-lived (greater than 10 µs) spin coherence. However, we observed no effect of 0.1-100 kHz radiofrequency (RF) fields on the orientation of night-migratory Eurasian blackcaps (Sylvia atricapilla). This suggests that the lifetime of the spin coherence involved in magnetoreception is shorter than the period of the highest frequency RF fields used in this experiment (i.e. approx. 10 µs). This result, in combination with an earlier study showing that 20-450 kHz electromagnetic fields disrupt magnetic compass orientation, suggests that the spin coherence lifetime of the magnetically sensitive radical pair is in the range 2-10 µs.

Natural abundance O17 and S33 nuclear magnetic resonance spectroscopy in solids achieved through extended coherence lifetimes

We have found that the NMR coherence lifetime ${T}_{2}$ of the symmetric central $\left(\ifmmode\pm\else\textpm\fi{}\frac{1}{2}\ensuremath{\rightarrow}\ensuremath{\mp}\frac{1}{2}\right)$ transition for $^{17}\mathrm{O}$ nuclei through a $\ensuremath{\pi}$ pulse train can be extended by over two orders of magnitude in a lattice dilute with NMR active nuclei through the use of highly selective (low-power) radio-frequency pulses. Crucial to this lifetime extension is the avoidance of coherence transfer to short-lived nonsymmetric transitions. For $^{17}\mathrm{O}$ in $\ensuremath{\alpha}$-quartz, we obtain ${T}_{2}=262\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.28em}{0ex}}\text{s}$. This translates into enormous sensitivity gains for echo train acquisition schemes such as Carr-Purcell-Meiboom-Gill (CPMG). By combining satellite population transfer schemes with a low-power (2.73 kHz) CPMG on $^{17}\mathrm{O}$ in quartz, we obtain over a 1000-fold sensitivity enhancement compared to a spectrum from a free induction decay acquired at a more typical rf field strength of $32.5\phantom{\rule{4.pt}{0ex}}\text{kHz}$. For $^{33}\mathrm{S}$ in ${\mathrm{K}}_{2}{\mathrm{SO}}_{4}$ the same approach yields ${T}_{2}=8.8\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{4pt}{0ex}}\mathrm{s}$ and a sensitivity enhancement of 63. In both examples, these enhancements enable the acquisition of NMR spectra at 9.4 T, despite their low natural abundance and spin-lattice relaxation times of $\ensuremath{\sim}900$ and $25\phantom{\rule{4.pt}{0ex}}\text{s}$, respectively, with signal-to-noise ratios of $\ensuremath{\sim}30$ in 1 h.

Does electronic coherence enhance anticorrelated pigment vibrations under realistic conditions?

The light-harvesting efficiency of a photoactive molecular complex is largely determined by the properties of its electronic quantum states. Those, in turn, are influenced by molecular vibrational states of the nuclear degrees of freedom. Here, we reexamine two recently formulated concepts that a coherent vibronic coupling between molecular states would either extend the electronic coherence lifetime or enhance the amplitude of the anticorrelated vibrational mode at longer times. For this, we study a vibronically coupled dimer and calculate the nonlinear two-dimensional (2D) electronic spectra that directly reveal electronic coherence. The time scale of electronic coherence is initially extracted by measuring the antidiagonal bandwidth of the central peak in the 2D spectrum at zero waiting time. Based on the residual analysis, we identify small-amplitude long-lived oscillations in the cross-peaks, which, however, are solely due to groundstate vibrational coherence, regardless of having resonant or off-resonant conditions. Our studies neither show an enhancement of the electronic quantum coherence nor an enhancement of the anticorrelated vibrational mode by the vibronic coupling under ambient conditions.

On the optimal relative orientation of radicals in the cryptochrome magnetic compass

Birds appear to be equipped with an innate magnetic compass. One biophysical model of this sense relies on spin dynamics in photogenerated radical pairs in the protein cryptochrome. This study employs a systematic approach to predict the dependence of the compass sensitivity on the relative orientation of the constituent radicals for spin systems comprising up to 21 hyperfine interactions. Evaluating measures of compass sensitivity (anisotropy) and precision (optimality) derived from the singlet yield, we find the ideal relative orientations for the radical pairs consisting of the flavin anion (F•−) coupled with a tryptophan cation (W•+) or tyrosine radical (Y•). For the geomagnetic field, the two measures are found to be anticorrelated in [F•− W•+]. The angle spanned by the normals to the aromatic planes of the radicals is the decisive parameter determining the compass sensitivity. The third tryptophan of the tryptophan triad/tetrad, which has been implicated with magnetosensitive responses, exhibits a comparably large anisotropy, but unfavorable optimality. Its anisotropy could be boosted by an additional ∼50% by optimizing the relative orientation of the radicals. For a coherent lifetime of 1 µs, the maximal relative anisotropy of [F•− W•+] is 0.27%. [F•− Y•] radical pairs outperform [F•− W•+] for most relative orientations. Furthermore, anisotropy and optimality can be simultaneously maximized. The entanglement decays rapidly, implicating it as a situational by-product rather than a fundamental driver within the avian compass. In magnetic fields of higher intensity, the relative orientation of radicals in [F•− W•+] is less important than for the geomagnetic field.

Electron Spin Coherence in Optically Excited States of Rare-Earth Ions for Microwave to Optical Quantum Transducers.

Efficient and reversible optical to microwave transducers are required for entanglement transfer between superconducting qubits and light in quantum networks. Rare-earth-doped crystals with narrow optical and spin transitions are a promising system for enabling these devices. Current resonant transduction approaches use ground-state electron spin transitions that have coherence lifetimes often limited by spin flip-flop processes and spectral diffusion, even at very low temperatures. We investigate spin coherence in an optically excited state of an Er^{3+}: Y_{2}SiO_{5} crystal at temperatures from 1.6 to 3.5K for a low 8.7mT magnetic field compatible with superconducting resonators. Spin coherence and population lifetimes of up to 1.6 μs and 1.2ms, respectively, are measured by optically detected spin echo experiments. Analysis of decoherence processes suggest that ms coherence can be reached at lower temperatures for the excited-state spins, whereas ground-state spin coherence would be limited to a few μs due to resonant interactions with other Er^{3+} spins in the lattice and greater instantaneous spectral diffusion from the radio-frequency control pulses. We propose a quantum transducer scheme with potential for close to unity efficiency that exploits the advantages offered by spin states of the optically excited electronic energy levels.

Room Temperature Broadband Polariton Lasing from a Dye‐Filled Microcavity

AbstractA material system is proposed to generate polariton lasing at room temperature over a broad spectral range. The system developed is based on a boron‐dipyrromethene fluorescent dye (BODIPY‐G1) that is dispersed into a polystyrene matrix and used as the active layer of a strongly coupled microcavity. It is shown that the BODIPY‐G1 exciton polaritons undergo nonlinear emission over a broad range of exciton–cavity mode detuning in the green‐yellow portion of the visible spectrum, with polariton lasing achieved over a spectral range spanning 33 nm. The recorded linewidth of ≈0.1 nm corresponds to a condensate coherence lifetime of ≈1 ps. It is proposed that similar effects can be anticipated using a range of molecular dyes in the BODIPY family; a result that paves the way for tunable polariton devices over the visible and near‐infrared spectral region.

A vector atomic magnetometer based on the spin self-sustaining Larmor method

Abstract We demonstrate a three-axis atomic magnetometer capable of measuring the magnitude and direction of a magnetic field based on the spin self-sustaining method using a rubidium vapor. Vectorial capability is added by precise compensation in three components of the magnetic field since the Larmor precession frequency is stable and constant in this process. A mean sensitivity of 0.78 pT/ Hz in the measurement of the field magnitude and a sensitivity of 3.5 × 10 - 6 rad/ Hz in the measurement of direction are realized. The coherence lifetime of atomic spins is lengthened to 340 ms and the sensitivity improves with time following a much faster τ - 1 rule which enables the magnetometer to reach the quantum shot noise floor in a much shorter time.

Deep and persistent spectral holes in thulium-doped yttrium orthosilicate for imaging applications

With their optical wavelength in the near infrared (790-800nm) and their unique spectroscopic properties at cryogenic temperatures, thulium-doped crystals are at the center of many architectures linked to classical signal processing and quantum information. In this work, we focus on Tm-doped YSO, a compound that was left aside in the mid-1990s due to its rather short optical coherence lifetime. By means of time-resolved hole-burning spectroscopy, we investigate the anisotropic enhanced nuclear Zeeman effect and demonstrate deep, sub-MHz, persistent spectral hole burning under specific magnetic field orientation and magnitude. By estimating the experimental parameters corresponding to a real-scale ultrasound optical tomography setup using Tm:YSO as a spectral filter, we validate Tm:YSO as a promising compound for medical imaging in the human body.

Single hole spin relaxation probed by fast single-shot latched charge sensing

Hole spins have recently emerged as attractive candidates for solid-state qubits for quantum computing. Their state can be manipulated electrically by taking advantage of the strong spin-orbit interaction (SOI). Crucially, these systems promise longer spin coherence lifetimes owing to their weak interactions with nuclear spins as compared to electron spin qubits. Here we measure the spin relaxation time T1 of a single hole in a GaAs gated lateral double quantum dot device. We propose a protocol converting the spin state into long-lived charge configurations by the SOI-assisted spin-flip tunneling between dots. By interrogating the system with a charge detector we extract the magnetic-field dependence of T1 ∝ B−5 for fields larger than B = 0.5 T, suggesting the phonon-assisted Dresselhaus SOI as the relaxation channel. This coupling limits the measured values of T1 from ~400 ns at B = 1.5 T up to ~60 μs at B = 0.5 T.

Observation of Angular Dependence of T1 in the Human White Matter at 3T.

Multiple factors including chemical composition and microstructure influence relaxivity of tissue water in vivo. We have quantified T1 in the human white mater (WM) together with diffusion tensor imaging to study a possible relationship between water T1, diffusional fractional anisotropy (FA) and fibre-to-field angle. An inversion recovery (IR) pulse sequence with 6 inversion times for T1 and a multi-band diffusion tensor sequence with 60 diffusion sensitizing gradient directions for FA and the fibre-to-field angle θ (between the principal direction of diffusion and B0) were used at 3 Tesla in 40 healthy subjects. T1 was assessed using the method previously applied to anisotropy of coherence lifetime to provide a heuristic demonstration as a surface plot of T1 as a function of FA and the angle θ. Our data show that in the WM voxels with FA > 0.3 T1 becomes longer (i.e. 1/T1 = R1 slower) when fibre-to-field angle is 50-60°, approximating the magic angle of 54.7°. The longer T1 around the magic angle was found in a number of WM tracts independent of anatomy. S0 signal intensity, computed from IR fits, mirrored that of T1 being greater in the WM voxels when the fibre-to-field angle was 50-60°. The current data point to fibre-to-field-angle dependent T1 relaxation in WM as an indication of effects of microstructure on the longitudinal relaxation of water.

Enhanced 1H-X D-HMQC performance through improved 1H homonuclear decoupling

The sensitivity of solid-state NMR experiments that utilize 1H zero-quantum heteronuclear dipolar recoupling, such as D-HMQC, is compromised by poor homonuclear decoupling. This leads to a rapid decay of recoupled magnetization and an inefficient recoupling of long-range dipolar interactions, especially for nuclides with low gyromagnetic ratios. We investigated the use, in symmetry-based 1H heteronuclear recoupling sequences, of a basic R element that was principally designed for efficient homonuclear decoupling. By shortening the time required to suppress the effects of homonuclear dipolar interactions to the duration of a single inversion pulse, spin diffusion was effectively quenched and long-lived recoupled coherence lifetimes could be obtained. We show, both theoretically and experimentally, that these modified sequences can yield considerable sensitivity improvements over the current state-of-the-art methods and applied them to the indirect detection of 89Y in a metal-organic framework.

Electronic coherence lifetimes of the Fenna-Matthews-Olson complex and light harvesting complex II.

The study of coherence between excitonic states in naturally occurring photosynthetic systems offers tantalizing prospects of uncovering mechanisms of efficient energy transport. However, experimental evidence of functionally relevant coherences in wild-type proteins has been tentative, leading to uncertainty in their importance at physiological conditions. Here, we extract the electronic coherence lifetime and frequency using a signal subtraction procedure in two model pigment-protein-complexes (PPCs), light harvesting complex II (LH2) and the Fenna-Matthews-Olson complex (FMO), and find that the coherence lifetimes occur at the same timescale (<100 fs) as energy transport between states at the energy level difference equal to the coherence energy. The pigment monomer bacteriochlorophyll a (BChla) shows no electronic coherences, supporting our methodology of removing long-lived vibrational coherences that have obfuscated previous assignments. This correlation of timescales and energy between coherences and energy transport reestablishes the time and energy scales that quantum processes may play a role in energy transport.

Linear and nonlinear coherent coupling in a Bell-Bloom magnetometer

Spin-exchange collisions in hot vapours are generally regarded as a decoherence mechanism. In contrast, we show that linear and non-linear spin-exchange coupling can lead to the generation of atomic coherence in a Bell-Bloom magnetometer. In particular, we theoretically and experimentally demonstrate that non-linear spin exchange coupling, acting in an analogous way to a wave-mixing mechanism, can create new modes of coherent excitation which inherit the magnetic properties of the natural Larmor coherence. The generated coherences further couple via linear spin-exchange interaction, leading to an increase of the natural coherence lifetime of the system. Notably, the measurements are performed in a low-density caesium vapour and for non-zero magnetic field, outside the standard conditions for collisional coherence transfer. The strategies discussed are important for the development of spin-exchange coupling into a resource for an improved measurement platform based on room-temperature alkali-metal vapours.