We experimentally demonstrate subwavelength spatial confinement of optical excitation using variants of stimulated Raman adiabatic passage (STIRAP) in a Pr 3 + : Y 2 SiO 5 crystal. Building on conventional STIRAP, we implement two more advanced schemes, double STIRAP and tripod STIRAP, which enable enhanced spatial control. At the cost of reduced coherence, double STIRAP provides an almost twofold improvement in resolution compared with conventional STIRAP, which already enables localization nearly two orders of magnitude below the pump beam waist. To resolve such fine structures near the diffraction limit, we employ an autocorrelation-based measurement technique. With this setup, we demonstrate excitation confinement by conventional STIRAP down to 260 ± 40 nm , thus achieving subwavelength localization. As another powerful variant of adiabatic passage, we apply tripod STIRAP using an additional donut-shaped control beam that suppresses population transfer outside the beam center via coherent population trapping. With tripod STIRAP, we generate excitations as narrow as 350 ± 40 nm , a factor of 28 below the width of the driving control beam. We demonstrate the scalability of the method by preparing tightly packed grids with up to 41 excitation spots without crosstalk, making the method well-suited for quantum architectures. Our results establish STIRAP variants as robust, versatile tools for coherent, spatially selective optical excitation on a subwavelength scale, opening broad applications in quantum technologies and classical optics.
We experimentally demonstrate subwavelength spatial confinement of optical excitation using variants of stimulated Raman adiabatic passage (STIRAP) in a Pr 3 + : Y 2 SiO 5 crystal. Building on conventional STIRAP, we implement two more advanced schemes, double STIRAP and tripod STIRAP, which enable enhanced spatial control. At the cost of reduced coherence, double STIRAP provides an almost twofold improvement in resolution compared with conventional STIRAP, which already enables localization nearly two orders of magnitude below the pump beam waist. To resolve such fine structures near the diffraction limit, we employ an autocorrelation-based measurement technique. With this setup, we demonstrate excitation confinement by conventional STIRAP down to 260 ± 40 nm , thus achieving subwavelength localization. As another powerful variant of adiabatic passage, we apply tripod STIRAP using an additional donut-shaped control beam that suppresses population transfer outside the beam center via coherent population trapping. With tripod STIRAP, we generate excitations as narrow as 350 ± 40 nm , a factor of 28 below the width of the driving control beam. We demonstrate the scalability of the method by preparing tightly packed grids with up to 41 excitation spots without crosstalk, making the method well-suited for quantum architectures. Our results establish STIRAP variants as robust, versatile tools for coherent, spatially selective optical excitation on a subwavelength scale, opening broad applications in quantum technologies and classical optics.
We experimentally demonstrated strong spatial confinement of optical excitations in Pr:YSO using two complementary coherent approaches: adiabatic passage techniques, namely STIRAP, double STIRAP, and tripod STIRAP, and broadband composite pulse (BCP) sequences. Both methods exploit the nonlinear response of coherent population transfer to transform a laser beam profile into a spatial filter, enabling localization of optical excitations far below the driving beam diameter. With conventional STIRAP, we achieved subwavelength localization down to 260 nm—only 2% of the pump beam diameter and more than a factor of two below the laser wavelength of 606 nm—representing a substantial improvement over previous demonstrations. At this confinement, the mean transverse ion occupancy drops below unity, placing our experiments in the single-ion addressing regime. Double STIRAP can further tighten confinement to below 1.4% of the beam diameter, albeit with loss of coherence due to the intermediate cleaning step, and can in principle be iterated for even stronger localization. Tripod STIRAP, by contrast, preserves coherence throughout the entire process while localizing population directly in a target state. In our experiment we achieved subwavelength confinement down to 350 nm, i.e., 3.5% of the control beam diameter, and crucially the sequential preparation of two-dimensional excitation patterns, demonstrated with grids of up to 41 individual spots without crosstalk between neighboring sites. To resolve these sub-imaging-resolution structures, we developed an autocorrelation-based measurement technique that showed excellent agreement with numerical simulations across all three STIRAP variants. As a second approach, we developed and implemented novel inhomogeneity-optimized BCP sequences tailored to the inhomogeneously broadened transitions of Pr:YSO. These sequences suppress the detuning-induced sideband artifacts that render previously proposed BCPs impractical in solid-state media, while maintaining high excitation efficiency over a wide range of pulse areas. Using IHO BCPs driven by a single donut-shaped laser beam, we confined optical excitations to 11% of the single-pulse excitation width—more than a factor of two improvement over previous narrowband composite pulse approaches, with a convergence rate of α = 0.68. We further tested BCP type II sequences that exploit variable pulse areas as additional control parameters, achieving localization down to 6% of the π-pulse excitation width at α = 0.95, albeit at the expense of increased detuning sensitivity. The current absolute widths of around 15 µm reflect the large beam waist chosen for imaging compatibility rather than a fundamental limit. Subwavelength confinement is readily achievable with tighter focusing. A systematic comparison of all techniques—including STED, RESOLFT, and EIT-based methods from literature—revealed that the coherent techniques developed in this work occupy a uniquely favorable region of capability space. STIRAP achieves the tightest relative confinement of any technique surveyed, which we attribute to the threshold nature of adiabatic passage and the resulting collapse of the numerator in the localization formula—a convergence channel unavailable to incoherent methods. Tripod STIRAP comes closest to satisfying all practical criteria simultaneously with coherence preservation, subwavelength confinement, demonstrated two-dimensional patterning, and long-lived storage. The CP approach complements these adiabatic techniques with single-laser simplicity and a direct path toward spatially selective quantum gate operations. Taken together, these results establish STIRAP-based techniques and BCP sequences as powerful and complementary tools for coherently preparing, addressing, and manipulating optical excitations on deep subwavelength scales. These capabilities are directly relevant to quantum memories, scalable qubit addressing in rare-earth crystals, and enhanced light–matter interactions at the nanoscale.
Abstract We experimentally demonstrate spatial confinement of atomic excitation by adiabatic passage processes in a rare-earth ion-doped Pr3+:Y2SiO5 crystal. In particular, we apply stimulated Raman adiabatic passage (STIRAP) and compare its performance with electromagnetically induced transparency (EIT). Using a Stokes beam with Gaussian and a pump beam with donut shape we localize the atomic population in the zero-intensity center of the latter. Our data confirm that adiabatic passage confines excitation far below the diameter of the driving laser beams, and that this localization rapidly increases with laser intensity. We find, that STIRAP significantly outperforms EIT, as it was predicted by previous theory proposals, i.e., STIRAP reaches small excitation volumes with much lower laser intensity. The experimental data agree very well with numerical simulations. The findings serve as a step towards new applications for STIRAP, to prepare excitation regions or population patterns in space with large resolution.
We consider a method of sub-wavelength superlocalization and patterning of atomic matter waves via a two dimensional stimulated Raman adiabatic passage (2D STIRAP) process. An atom initially prepared in its ground level interacts with a doughnut-shaped optical vortex pump beam and a traveling wave Stokes laser beam with a constant (top-hat) intensity profile in space. The beams are sent in a counter-intuitive temporal sequence, in which the Stokes pulse precedes the pump pulse. The atoms interacting with both the traveling wave and the vortex beam are transferred to a final state through the 2D STIRAP, while those located at the core of the vortex beam remain in the initial state, creating a super-narrow nanometer scale atomic spot in the spatial distribution of ground state atoms. By numerical simulations we show that the 2D STIRAP approach outperforms the established method of coherent population trapping, yielding much stronger confinement of atomic excitation. Numerical simulations of the Gross-Pitaevskii equation show that using such a method one can create 2D bright and dark solitonic structures in trapped Bose-Einstein condensates (BECs). The method allows one to circumvent the restriction set by the diffraction limit inherent to conventional methods for formation of localized solitons, with a full control over the position and size of nanometer resolution defects.
We report on experimental investigations of stimulated Raman adiabatic passage (STIRAP) in a Pr3+:Y2SiO5 crystal. STIRAP drives complete, coherent population transfer between two hyperfine levels in the Pr3+ ions. We investigate the variation of the STIRAP transfer efficiency with the experimental parameters: e.g., detunings, Rabi frequencies, and pulse delays. In addition, we also observe an alternative and efficient, adiabatic transfer process---i.e., b-STIRAP---which occurs for a reversed sequence of laser pulses. We compare the efficiencies and time-resolved transfer dynamics of STIRAP and b-STIRAP. The experimental data are supported by numerical simulations, also including the effect of laser frequency jitter. Our experimental data and the numerical simulations provide a clear and convincing demonstration of adiabatic excitations in a solid medium.
We experimentally demonstrate composite stimulated Raman adiabatic passage (CSTIRAP), which combines the concepts of composite pulse sequences and adiabatic passage. The technique is applied for population transfer in a rare-earth doped solid. We compare the performance of CSTIRAP with conventional single and repeated STIRAP, either in the resonant or the highly detuned regime. In the latter case, CSTIRAP improves the peak transfer efficiency and robustness, boosting the transfer efficiency substantially compared to repeated STIRAP. We also propose and demonstrate a universal version of CSTIRAP, which shows improved performance compared to the originally proposed composite version. Our findings pave the way towards new STIRAP applications, which require repeated excitation cycles, e.g., for momentum transfer in atom optics, or dynamical decoupling to invert arbitrary superposition states in quantum memories.
We experimentally demonstrate spatial confinement of optically driven atomic excitation by broadband composite pulses in a rare-earth ion-doped Pr 3 + : Y 2 SiO 5 crystal. The experimental data confirm that such sequences enable spatially localized excitation well below the diameter of the applied laser beam, with a substantial improvement compared to previous developments and applications of other classes of composite pulses. In particular, we derived and applied broadband composite sequences, which also work efficiently in inhomogeneously broadened media, while also maintaining robustness with regard to fluctuations of the driving laser intensity. We perform extensive measurements to assess and compare the performance of several classes of broadband composite sequences. The findings are confirmed by numerical simulations, which agree very well with the experimental data. As the concepts are also applicable to spatially confined excitations below the diffraction limit of the laser beam, the results serve as an important step towards high-resolution imaging, preparation and addressing in quantum technologies and classical applied optics.