Abstract We demonstrate the precise in situ measurement of extreme-high vacuum (XHV) in a cryogenic linear Paul trap operating at 5.7 K, utilizing laser-cooled Be + Coulomb crystals as dual-mode quantum probes. Two independent methods, elastic collision rate monitoring and reaction rate analysis, were employed to determine the vacuum level within the cryogenic linear Paul trap. Based on the collision rate of a single trapped beryllium ion with background gas, which was measured as 1.3(7) × 10 −4 Hz, the pressure under cryogenic conditions was calculated to be 6.0(3.4) × 10 −12 Pa. Alternatively, by leveraging the reaction rate of Be + ions with background gases, a pressure of 8.4(1) × 10 −12 Pa was obtained. The mutual agreement between these two methods validates the reliability of cold-atom-based vacuum metrology at the 10 −12 Pa scale, successfully overcoming the detection limits of conventional vacuum gauges. This approach, which capitalizes on the unique mass properties and photostability of Be + ions, fills a critical gap in XHV metrology and paves the way for the development of chip-trap-integrated in situ vacuum sensing technologies.
Abstract We demonstrate the precise in situ measurement of extreme-high vacuum (XHV) in a cryogenic linear Paul trap operating at 5.7 K, utilizing laser-cooled Be + Coulomb crystals as dual-mode quantum probes. Two independent methods, elastic collision rate monitoring and reaction rate analysis, were employed to determine the vacuum level within the cryogenic linear Paul trap. Based on the collision rate of a single trapped beryllium ion with background gas, which was measured as 1.3(7) × 10 −4 Hz, the pressure under cryogenic conditions was calculated to be 6.0(3.4) × 10 −12 Pa. Alternatively, by leveraging the reaction rate of Be + ions with background gases, a pressure of 8.4(1) × 10 −12 Pa was obtained. The mutual agreement between these two methods validates the reliability of cold-atom-based vacuum metrology at the 10 −12 Pa scale, successfully overcoming the detection limits of conventional vacuum gauges. This approach, which capitalizes on the unique mass properties and photostability of Be + ions, fills a critical gap in XHV metrology and paves the way for the development of chip-trap-integrated in situ vacuum sensing technologies.
Trapped-ion systems are among the most promising hardware candidates for large scale quantum computing and quantum simulation. In order to scale up such devices, it is necessary to engineer extreme-high vacuum (XHV) environments to prevent background gas from disrupting the ion crystal. Here we present a new cryogenic ion trapping system designed for long time storage of large ion chains. Our apparatus is based on a segmented-blade ion trap enclosed in a 4 K cryostat, which enables us to routinely trap and hold over 100 171 Yb + ions for hours in a linear configuration, due to low background gas pressure from differential cryo-pumping. We characterize the XHV cryogenic environment measuring pressures below by recording both inelastic and elastic collisions between the ion chain and the molecular background gas. We also demonstrate coherent one and two-qubit operations and nearly equidistant ion spacing for chains of up to 44 ions using anharmonic axial potentials, in order to enable better detection and single ion addressing in large ion arrays. We anticipate that this reliable production and lifetime enhancement of large linear ion chains will enable quantum simulation of models that are intractable with classical computer modeling.
Ultra-high vacuum conditions are ideal for the study of trapped ions. They offer an almost perturbation-free environment, where ions confined in traps can be studied for extended periods of time-facilitating precision measurements and allowing infrequent events to be observed. However, if one wishes to study processes involving molecular ions, it is important to consider the effect of blackbody radiation (BBR). The vast majority of molecular ions interact with BBR. At 300 K, state selection in trapped molecular ions can be rapidly lost (in a matter of seconds). To address this issue, and to maintain state selectivity in trapped molecular ions, a cryogenic ion trap chamber has been constructed and characterized. At the center of the apparatus is a linear Paul ion trap, where Coulomb crystals can be formed for ion-neutral reaction studies. Optical access is provided, for lasers and for imaging of the crystals, alongside ion optics and a flight tube for recording time-of-flight mass spectra. The ion trap region, encased within two nested temperature stages, reaches temperatures below 9 K. To avoid vibrations from the cryocooler impeding laser cooling or imaging of the ions, vibration-damping elements are explicitly included. These components successfully inhibit the coupling of vibrations from the cold head to the ion trap-confirmed by accelerometer measurements and by the resolution of images recorded at the trap center (at 9 and 295 K). These results confirm that the cryogenic ion trap apparatus meets all requirements for studying ion-neutral reactions under cold, controlled conditions.
We present a room-temperature Extreme High Vacuum (XHV) system engineered to support the long-duration operation of a trapped-ion quantum processor. Background-gas collisions impose limitations on trapped-ion performance and scalability by interrupting algorithmic execution and, in some cases, ejecting ions from the trap. Using molecular-flow simulations, we optimize the chamber geometry, conductance pathways, and pumping configuration to maximize the effective pumping speed at the ion location. We perform high-temperature heat treatment of stainless steel vacuum components to achieve the desired outgassing rate, guided by quantitative relations of bulk diffusive processes, allowing us to reduce the H2 outgassing load to the 10−15mbarls−1cm−2 level. The final pressure in our chamber, measured by a hot cathode gauge, is 1.5×10−12mbar, corresponding to the gauge's measurement limit. We measure the local pressure at the ion location by observing collision-induced reordering events in a long ion chain of mixed-isotope Yb+. From the observed reordering frequency, we extract the average interval between collisions to be (1.9±0.1)hrs/ion. This corresponds to a local pressure of (3.9±0.3)×10−12mbar at the ion location, assuming that all collisions arise from background H2 molecules at room temperature. Our demonstration extends the continuous operation time of a quantum processor while maintaining the simplicity of a room-temperature system that does not require cryogenic apparatus.
Ultra-high vacuum measurement and extremely high vacuum (UHV/XHV) measurement play an important role in high-tech fields such as deep space exploration, particle accelerators, and nanoscience; with the continuous extension of the lower limit of measurement, especially when it reaches the order of 10–10 Pa, higher requirements are placed on the accuracy of the measurement. At present, in the field of UHV/XHV measurement, ionization gauges based on the principle of neutral gas ionization are commonly applied to the vacuum measurement. However, traditional ionization vacuum gauges during use can create electronic excitation desorption effects, soft X-rays, and the effect of hot cathode outgassing, thereby affecting the accuracy of measurement and limiting the lower limit of measurement. Compared with the traditional measurement technology, this method uses the relationship between the loss rate and pressure caused by the collision of cold atoms trapped in the trap depth with the background gas to calculate the gas density and inversely calculate the vacuum pressure. Based on the intrinsic quantum mechanical properties of cold atom collisions, this method is expected to be developed into a new vacuum traceability standard. In this paper, based on the small-angle approximation and impulse approximation under the quantum scattering theory, the loss rate coefficient of the collision of 6Li cold atoms with background gas molecules is calculated. According to the ideal gas equation, the pressure inversion formula is obtained. The collision loss rate is extracted by accurately fitting the loss curve of the cold atom. In order to improve the accuracy of vacuum inversion and reduce the influence of quantum diffractive collision on loss rate measurement, the trap depth under the conditions of a certain cooling laser intensity, detuning, and magnetic field gradient is determined by the photoassociation method. Finally, in a range of 1 × 10–8–5 × 10–6 Pa, the inverted pressure value is compared with the measured value of the ionization meter, proving that this method has good accuracy and reliability in the inversion of vacuum pressure. At present, the main factor restricting the improvement of accuracy is the influence of the collision between the excited atoms in the magneto-optical trap and the background gas on the loss rate measurement. In the future, with the proportion of excited atoms and the excited state C6 coefficient to be precisely determined, the uncertainty of vacuum pressure measurement can be further reduced.
Electron beam ion traps used for spectroscopy of highly charged ions (HCI) produce a deep trapping potential leading to high temperatures of the stored ions, and thus limiting the achievable spectral resolution. A novel device at the Max-Planck-Institut für Kernphysik, the Cryogenic linear Paul Trap Experiment (CryPTEx), attached to an electron beam ion trap, provides a new experimental platform to overcome these limitations. The trap assembly operates at a temperature of 4 K and offers optical access for quantum manipulation and imaging of the trapped ions. Since forbidden optical transitions in HCI do not support direct laser cooling, sympathetic cooling with Coulomb crystals of singly charged ions such as Be+ or Mg+ will be applied in order to reach the natural linewidth of optical forbidden transitions in HCI of interest. With the added advantage of long ion trapping times resulting from residual gas pressures of H2 at 4 K below 10−15 mbar, CryPTEx has been commissioned in collaboration with the Ion Trap Group in Århus using rovibrationally cooled MgH+ ions. Strong suppression of the black body radiation at the trap center, ion storage times of about 28 hours, and largely enhanced population of the rovibrational ground state were achieved.
Storage and cooling of highly charged ions require ultra-high vacuum levels obtainable by means of cryogenic methods. We have developed a linear Paul trap operating at 4 K capable of very long ion storage times of about 30 h. A conservative upper bound of the H(2) partial pressure of about 10(-15) mbar (at 4 K) is obtained from this. External ion injection is possible and optimized optical access for lasers is provided, while exposure to black body radiation is minimized. First results of its operation with atomic and molecular ions are presented. An all-solid state laser system at 313 nm has been set up to provide cold Be(+) ions for sympathetic cooling of highly charged ions.