Efficient Optical Pumping Research Articles

Observation of Narrow Optical Homogeneous Linewidth and Long Nuclear Spin Lifetimes in a Prototypical [Eu(trensal)] Complex

Coherent light–matter interfaces are key elements for many quantum information processing architectures. Rare-earth ion (REI)-containing systems featuring narrow inter-configurational f–f transitions are suitable for creating such interfaces. Recently, narrow homogeneous linewidths (Γh) and long nuclear spin lifetimes (T1spin) associated with two Eu3+ complexes featuring the 5D0 → 7F0 f–f transition have been reported, elucidating that REI-molecule-based coherent light–matter interfaces can be obtained. In this study, we report a homogeneous linewidth of 2.8 MHz at 4.2 K, corresponding to an optical coherence lifetime (T2opt) of 114 ns (0.11 μs), associated with the 5D0 → 7F0 transition of the prototypical charge neutral Eu3+ complex─[Eu(trensal)]. Moreover, we have observed long nuclear spin lifetimes (T1spin) up to 460 ± 80 s at 4.2 K for the complex and efficient optical pumping of hyperfine levels of the 5D0 ground state. The results presented in this study indicate that narrow homogeneous linewidths and long nuclear spin lifetimes could be a generic property of molecular Eu3+ complexes featuring the 5D0 → 7F0 transition.

Dye-sensitized Er3+-doped CaF2 nanoparticles for enhanced near-infrared emission at 1.5 μm

Lanthanide (Ln)-doped nanoparticles have shown potential for applications in various fields. However, the weak and narrow absorption bands of the Ln ions ( Ln 3 + ), hamper efficient optical pumping and severely limit the emission intensity. Dye sensitization is a promising way to boost the near-infrared (NIR) emission of Er 3 + , hence promoting possible application in optical amplification at 1.5 μm, a region that is much sought after for telecommunication technology. Herein, we introduce the fluorescein isothiocyanate (FITC) organic dye with large absorption cross section as energy donor of small-sized ( ∼ 3.6 nm ) Er 3 + -doped CaF 2 nanoparticles. FITC molecules on the surface of CaF 2 work as antennas to efficiently absorb light, and provide the indirect sensitization of Er 3 + boosting its emission. In this paper, we employ photoluminescence and transient absorption spectroscopy, as well as density functional theory calculations, to provide an in-depth investigation of the FITC → Er 3 + energy transfer process. We show that an energy transfer efficiency of over 89% is achieved in CaF 2 : Er 3 + @ FITC nanoparticles resulting in a 28 times enhancement of the Er 3 + NIR emission with respect to bare CaF 2 : Er 3 + . Through the multidisciplinary approach used in our work, we are able to show that the reason for such high sensitization efficiency stems from the suitable size and geometry of the FITC dye with a localized transition dipole moment at a short distance from the surface of the nanoparticle.

Simultaneous preparation of two initial clock states in a thulium optical clock

Due to the low sensitivity of the thulium optical clock to black-body radiation and good accuracy and stability estimations, it appears to be one of the most promising transportable optical clocks. One of the leading systematic effects for Tm clock transition, namely the second-order Zeeman effect, can be canceled by probing two clock transitions between different hyperfine levels of ground and metastable states during the clock operation. We prepare the atoms in $m_F=0$ state of both ground hyperfine levels simultaneously and excite alternately two clock transitions. Here we demonstrate efficient optical pumping into both target states via single-frequency radiation at 418.8 nm. The resulting population of $m_F=0$ states of ground hyperfine levels is 36% and 3.8% of the initial number of atoms with less than 4% and 0.4% on non-zero magnetic sublevels, correspondingly. We performed numerical simulations of the optical pumping process which is able to explain experimental results reasonably well.

Optical spin polarization in ruby enhances slow light by high-contrast transient spectral hole-burning

The spin-lattice relaxation time in the 4 A 2 ground state of C r 3 + in ruby can be on the order of magnitude of seconds at liquid helium temperatures in low magnetic fields B | | c . This allows for highly efficient optical pumping of the spin levels in this system. Such pumping can then in turn be employed to drastically increase the optical density of the inhomogeneously broadened R 1 ( ± 3 / 2 ) or R 1 ( ± 1 / 2 ) lines and also to narrow the spectral hole width because Cr–Cr electron-spin flips (cross relaxation) are suppressed in the ground state, leading to longer dephasing times T 2 ∗ . Both effects can be employed to further reduce the group velocity of light pulses propagating through a transient spectral hole.

Optical isolator based on highly efficient optical pumping of Rb atoms in a miniaturized vapor cell

We demonstrate both numerically and experimentally the important role of buffer gas in achieving optical isolator based on efficient hyperfine-structure optical pumping of Rubidium (87Rb) atoms in miniaturized vapor cells. It is observed that the increase in the buffer gas pressure allows achieving highly efficient optical pumping. Specifically, at a buffer gas pressure of 40 Torr, it is possible to pump about 85% of the atoms out of the pumped state into the other ground state. While optical pumping has been reported for conventional centimeter-scale cells, we show that in miniaturized cells the role of buffer gas is crucial, as the higher collision rate with the walls diminishes the effect of optical pumping, posing a stringent limitation on the applicability of optical pumping in miniaturized systems. Following the results reported herein, we demonstrate an optical isolator with isolation ratio better than 20 dB at a relatively low temperature of about 80 °C, and with a low magnetic field (∼800 Gauss). The obtained results provide another step forward in the quest for miniaturizing quantum devices. The demonstrated device shows that such miniaturized vapor cells can be considered for applications such as all-optical switching, optical quantum memory, frequency references, and magnetometry to name a few.

Efficient optical pumping of alkaline atoms for evanescent fields at dielectric-vapor interfaces.

We experimentally demonstrate hyperfine optical pumping of rubidium atoms probed by an evanescent electromagnetic field at a dielectric-vapor interface. This light-atom interaction at the nanoscale is investigated using a right angle prism integrated with a vapor cell and excited by evanescent wave under total internal reflection. An efficient hyperfine optical pumping, leading to almost complete suppression of absorption on the probed evanescent signal, is observed when a pump laser beam is sent at normal incidence to the interface. In contrast, when the pump and probe beams are co-propagating in the integrated prism-vapor cell, no clear evidence of optical pumping is observed. The experimental results are supported by a detailed model based on the optical Bloch equation of a four atomic-level structure, which also includes a treatment of transit relaxation and wall collision with relaxation rates that were obtained directly from the thermal velocities of the atoms and the penetration depth of the evanescent wave. The obtained highly efficient optical pumping at the nanoscale is regarded as an important step in the quest for applications such as optical switching, magnetometry, and quantum memory.

Time-domain Ramsey-narrowed sub-kHz electromagnetically induced absorption in atomic potassium

The use of electromagnetically induced absorption (EIA) in sensing and metrology has been thus far hindered by saturation effects, which severely degrade its linewidth. Here we propose, and experimentally demonstrate, that time-dependent Ramsey spectroscopy in potassium vapour overcomes the detrimental effect of saturation. We observe sub-kHz Ramsey fringes, with full control of the EIA resonance characteristics. Combined with the efficient optical pumping associated to the K D1 line, the present work demonstrates an EIA scheme suitable for sensing and metrological applications.

Highly Efficient Optical Pumping of Spin Defects in Silicon Carbide for Stimulated Microwave Emission

Microwaves (MWs) are at the heart of many technologies, $e.g.$ for communication, timekeeping, remote sensing, and quantum information processing. Masers can boost faint MW signals quite nicely, but not under real-world conditions. The authors demonstrate efficient population inversion of optically pumped vacancy-related spins in SiC, at room temperature, and find realistic operating conditions for a SiC maser to serve as a continuous-wave amplifier. These spins can also be coherently coupled to superconducting cavities efficiently at cryogenic temperatures. These findings suggest this SiC system as a promising platform for MW photonics and quantum electronics.

Efficient optical pumping using hyperfine levels in 145Nd3+:Y2SiO5 and its application to optical storage

Efficient optical pumping is an important tool for state initialization in quantum technologies, such as optical quantum memories. In crystals doped with Kramers rare-earth ions, such as erbium and neodymium, efficient optical pumping is challenging due to the relatively short population lifetimes of the electronic Zeeman levels, of the order of 100 ms at around 4 K. In this article we show that optical pumping of the hyperfine levels in isotopically enriched 145Nd :Y2SiO5 crystals is more efficient, owing to the longer population relaxation times of hyperfine levels. By optically cycling the population many times through the excited state a nuclear spin flip can be forced in the ground state hyperfine manifold, in which case the population is trapped for several seconds before relaxing back to the pumped hyperfine level. To demonstrate the effectiveness of this approach in applications we perform an atomic frequency comb memory experiment with 33% storage efficiency in 145Nd :Y2SiO5, which is on a par with results obtained in non-Kramers ions, e.g. europium and praseodymium, where optical pumping is generally efficient due to the quenched electronic spin. Efficient optical pumping in neodymium-doped crystals is also of interest for spectral filtering in biomedical imaging, as neodymium has an absorption wavelength compatible with tissue imaging. In addition to these applications, our study is of interest for understanding spin dynamics in Kramers ions with nuclear spin.

Coherence time of over a second in a telecom-compatible quantum memory storage material

Quantum memories for light will be essential elements in future long-range quantum communication networks. These memories operate by reversibly mapping the quantum state of light onto the quantum transitions of a material system. For networks, the quantum coherence times of these transitions must be long compared to the network transmission times, approximately 100 ms for a global communication network. Due to a lack of a suitable storage material, a quantum memory that operates in the 1550 nm optical fiber communication band with a storage time greater than 1 us has not been demonstrated. Here we describe the spin dynamics of $^{167}$Er$^{3+}:$Y$_{2}$SiO$_{5}$ in a high magnetic field and demonstrate that this material has the characteristics for a practical quantum memory in the 1550 nm communication band. We observe a hyperfine coherence time of 1.3 seconds. Further, we demonstrate efficient optical pumping of the entire ensemble into a single hyperfine state, the first such demonstration in a rare-earth system and a requirement for broadband spin-wave storage. With an absorption of 70 dB/cm at 1538 nm and $\Lambda$-transitions enabling spin-wave storage, this material is the first candidate identified for an efficient, broadband quantum memory at telecommunication wavelengths.

Performance assessment of a new laser system for efficient spin exchange optical pumping in a spin maser measurement of 129Xe EDM

We demonstrate spin-exchange optical pumping of 129Xe atoms with our newly made laser system. The new laser system was prepared to provide higher laser power required for the stable operation of spin maser oscillations in the 129Xe EDM experiment. We studied the optimum cell temperature and pumping laser power to improve the degree of 129Xe spin polarization. The best performance was achieved at the cell temperature of 100 ∘C with the presently available laser power of 1 W. The results show that a more intense laser is required for further improvement of the spin polarization at higher cell temperatures in our experiment.

Rare-earth doped transparent ceramics for spectral filtering and quantum information processing

Homogeneous linewidths below 10 kHz are reported for the first time in high-quality Eu3+ doped Y 2O3 transparent ceramics. This result is obtained on the 7F0→5D0 transition in Eu3+ doped Y 2O3 ceramics and corresponds to an improvement of nearly one order of magnitude compared to previously reported values in transparent ceramics. Furthermore, we observed spectral hole lifetimes of ∼15 min that are long enough to enable efficient optical pumping of the nuclear hyperfine levels. Additionally, different Eu3+ concentrations (up to 1.0%) were studied, resulting in an increase of up to a factor of three in the peak absorption coefficient. These results suggest that transparent ceramics can be useful in applications where narrow and deep spectral holes can be burned into highly absorbing lines, such as quantum information processing and spectral filtering.

Effective collinear optical pumping for nuclear spin polarization

By numerically solving the density matrix equations, we show that the laser frequency ramping method by means of position-dependent Zeeman splitting can efficiently polarize nuclear spin of atoms/ions in an accelerator beamline. This minimizes a quantum phenomenon, coherent population trapping, which limits the optical pumping efficiency in the polarized beamline for radioactive nuclear spin polarization. We consider the Li8 atomic system interacting with two circularly polarized laser beams in the presence of time-dependent magnetic field. From numerical results, we find that optimum frequency ramping allows efficient optical pumping for a short interaction time, e.g., 2 μs.

Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field

Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots. The strong interaction of a single, optically injected electron spin with the nuclear spins acts as a stabilizing, effective magnetic field (Knight field) on the nuclei. We optically tune the Knight field amplitude and direction. In combination with a small transverse magnetic field, we are able to control the longitudinal and transverse components of the nuclear spin polarization in the absence of lattice strain—that is, in dots with strongly reduced static nuclear quadrupole effects, as reproduced by our model calculations.

Optical pumping in a microfabricated Rb vapor cell using a microfabricated Rb discharge light source

Miniature (<few cm3) vapor-cell based devices using optical pumping of alkali atoms, such as atomic clocks and magnetometers, today mostly employ vertical-cavity surface-emitting lasers as pump light sources. Here, we report on the demonstration of optical pumping in a microfabricated alkali vapor resonance cell using (1) a microfabricated Rb discharge lamp light source, as well as (2) a conventional glass-blown Rb discharge lamp. The microfabricated Rb lamp cell is a dielectric barrier discharge (DBD) light source, having the same inner cell volume of around 40 mm3 as that of the resonance cell, both filled with suitable buffer gases. A miniature (∼2 cm3 volume) test setup based on the Mz magnetometer interrogation technique was used for observation of optical-radiofrequency double-resonance signals, proving the suitability of the microfabricated discharge lamp to introduce efficient optical pumping. The pumping ability of this light source was found to be comparable to or even better than that of a conventional glass-blown lamp. The reported results indicate that the micro-fabricated DBD discharge lamp has a high potential for the development of a new class of miniature atomic clocks, magnetometers, and quantum sensors.

Efficient optical pumping and high optical depth in a hollow-core photonic-crystal fibre for a broadband quantum memory

The generation of large multiphoton quantum states—for applications in computing, metrology and simulation—requires a network of high-efficiency quantum memories capable of storing broadband pulses. Integrating these memories into a fibre offers a number of advantages towards realizing this goal: strong light–matter coupling at low powers, simplified alignment and compatibility with existing photonic architectures. Here, we introduce a large-core kagome-structured hollow-core fibre as a suitable platform for an integrated fibre-based quantum memory with a warm atomic vapour. We demonstrate, for the first time, efficient optical pumping in such a system, where 90 ± 1% of atoms are prepared in the ground state. We measure high optical depths (3 × 104) and narrow homogeneous linewidths (6 ± 2 MHz) that do not exhibit significant transit-time broadening, showing that we can prepare a Λ-level system in a pure state. Our results establish that kagome fibres are suitable for implementing a broadband, room-temperature quantum memory, as well as a range of nonlinear optical effects.

High-power top-hat pulses from a Yb master oscillator power amplifier for efficient optical parametric amplifier pumping

We demonstrate shaping of high-energy broadband Yb amplifier pulses for the generation of a (sub)picosecond top-hat temporal pulse profile that significantly improves pumping efficiency of an optical parametric amplifier (OPA). Phase-only modulation is applied by an acousto-optic programmable dispersion filter. This simple scheme is scalable to a high average power due to a relatively broad bandwidth of the Yb:CaF(2) gain medium used in the amplifier that supports a sub-150-fs transform-limited pulse duration. Additionally we show that OPA seeding with supercontinuum remains possible because top-hat-shaped pulses passed through a glass block recompress to ≈200 fs with minimum satellite production.

Triplet-singlet conversion in ultracoldCs2and production of ground-state molecules

We propose a process to convert ultracold metastable Cs$_2$ molecules in their lowest triplet state into (singlet) ground state molecules in their lowest vibrational levels. Molecules are first pumped into an excited triplet state, and the triplet-singlet conversion is facilitated by a two-step spontaneous decay through the coupled $A^{1}\Sigma_{u}^{+} \sim b ^{3}\Pi_{u}$ states. Using spectroscopic data and accurate quantum chemistry calculations for Cs$_2$ potential curves and transition dipole moments, we show that this process has a high rate and competes favorably with the single-photon decay back to the lowest triplet state. In addition, we demonstrate that this conversion process represents a loss channel for vibrational cooling of metastable triplet molecules, preventing an efficient optical pumping cycle down to low vibrational levels.

Facile production of up-converted quantum dot lasers

We report a facile production of an up-converted surface-emitting DFB laser, performed by exploiting the versatility of sol-gel chemistry, the intriguing properties of well designed graded CdSe-CdS-Cd(0.5)Zn(0.5)S-ZnS colloidal quantum dots, and the scalability of nanoimprinting. Our laser prototype operates in the visible region following efficient optical pumping by either direct one-photon excitation or through the up-conversion of near infrared (NIR) light. By achieving cavity mode Q-factors in excess of 650 and retaining high lasing stabilities in air, this work highlights the feasibility of creating integrated lasing devices through solution based methods.

Optically end-pumped plastic waveguide laser with in-line Fabry-Pérot resonator

A plastic waveguide laser doped with organic dye molecule was fabricated with self-written active (SWA) waveguide technique. The device has a Fabry-Perot resonator consisting of a pair of highly reflective dielectric mirrors, which has brought two advantages for efficient optical pumping; (i) the efficient optical feedback in the cavity can be induced, and (ii) the reflection band of the dielectric mirrors can be tuned to overlap only with the emission band of the doped dye. For the SWA waveguide devices, furthermore, the active waveguide core is essentially coupled with a fiber port for optical input. Owing to these advantages, an experimental configuration for the optical end pumping can be easily applied. The high absorption efficiency for the pumping light could be obtained in this pumping method. A remarkable lowering of the lasing threshold was observed. As the best results of this study, consequently, the lasing action under the optical pumping energy as low as 50 nJ was achieved.