Micromotion Compensation Research Articles

Enhanced micromotion compensation using a phase-modulated light field

Enhanced micromotion compensation using a phase-modulated light field

Precise micromotion compensation of a tilted ion chain

Excess micromotion can be a substantial source of errors in trapped-ion based quantum processors and clocks due to the sensitivity of the internal states of the ion to external fields and motion. This problem can be fixed by compensating background electric fields in order to position ions at the RF node and minimize their driven micromotion. Here we describe techniques for compensating ion chains in scalable surface ion traps. These traps are capable of cancelling stray electric fields with fine spatial resolution in order to compensate multiple closely spaced ions due to their large number of relatively small control electrodes. We demonstrate a technique that compensates an ion chain to better than 5 V/m and within 0.1 degrees of chain rotation.

Micromotion compensation of trapped ions by qubit transition and direct scanning of dc voltages.

Excess micromotion is detrimental to accurate qubit control of trapped ions, thus measuring and minimizing it is crucial. In this paper, we present a simple approach for measuring and suppressing excess micromotion of trapped ions by leveraging the existing laser-driven qubit transition scheme combined with direct scanning of dc voltages. The compensation voltage is deduced by analyzing the Bessel expansion of a scanned qubit transition rate. The method provides a fair level of sensitivity for practical quantum computing applications, while demanding minimal deviation of trap condition. By accomplishing compensation of excess micromotion in the qubit momentum-excitation direction, the scheme offers an additional avenue for excess micromotion compensation, complementing existing compensation schemes.

Numerical investigation of a segmented-blade ion trap with biasing rods

We report a numerical study of a linear ion trap that has segmented blades and biasing rods. Our system consists of radio frequency (rf) blades, dc blades with ten separate electrodes, and two biasing rods for compensating the ions' micromotion. After calculating the optical access for the ions, we find rf and dc voltages that result in a stable trapping configuration of $^{171}$Yb$^{+}$ ions. We also explore the micromotion compensation with the biasing rods, and calculate the influence of blade misalignment to the trap potential. Our work offers quantitative understanding of the trap architecture, assisting reliable operation of an ion-trap quantum computer.

Measurement of ion displacement via RF power variation for excess micromotion compensation

We demonstrate a method of micromotion minimization of a trapped ion in a linear Paul trap based on the precision measurement of the ion trapping position displacement due to a stray electric field in the radial plane by ion fluorescence imaging. The amount of displacement in the radial plane is proportional to the strength of a stray electric field. Therefore, we evaluated the micromotion compensation condition by measuring the ion displacements from the ion equilibrium position using two different radial trap frequencies with various combinations of the compensation voltage. The residual electric field uncertainty of this technique reached a few volts per meter. This compensation technique does not depend on the orientation of the incident cooling laser or the detuning and imaging direction. Therefore, this method is suitable for a planar ion trap, a stylus ion trap, which limits the propagation angle of lasers, or miniaturized ion trap systems for sensing and metrological applications.

High-energy-resolution measurements of an ultracold-atom–ion collisional cross section

The cross section of a given process fundamentally quantifies the probability for that given process to occur. In the quantum regime of low energies, the cross section can vary strongly with collision energy due to quantum effects. Here, we report on a method to directly measure the atom-ion collisional cross section in the energy range of 0.2-12 mK$\cdot$ k$_B$, by shuttling ultracold atoms trapped in an optical-lattice across a radio-frequency trapped ion. In this method, the average number of atom-ion collisions per experiment is below one such that the energy resolution is not limited by the broad (power-law) steady-state atom-ion energy distribution. Here, we estimate that the energy resolution is below 200 $\mu$K$\cdot$k$_B$, limited by drifts in the ion's excess micromotion compensation and can be reduced to the 10's $\mu$K$\cdot$k$_B$ regime. This resolution is one order-of-magnitude better than previous experiments measuring cold atom-ion collisional cross section energy dependence. We used our method to measure the energy dependence of the inelastic collision cross sections of a non-adiabatic Electronic-Excitation-Exchange (EEE) and Spin-Orbit Change (SOC) processes. We found that in the measured energy range, the EEE and SOC cross sections statistically agree with the classical Langevin cross section. This method allows for measuring the cross sections of various inelastic processes and opens up possibilities to search for atom-ion quantum signatures such as shape-resonances.

Excess micromotion compensation of trapped ions in a linear Paul trap for trace isotope analysis

ABSTRACTExcess micromotion of trapped calcium ions was detected and compensated in our linear Paul trap apparatus for trace isotope analysis. The micromotion was detected by Charge-coupled device (CCD). camera and radio frequency (rf) correlation method. We found that 230 and 2280 V of compensation voltages were needed for x- and y-axis compensation in our apparatus, respectively. The z-axis micromotion was confirmed by the experiment and its cause was investigated by finding a shape of z-axis confinement field. The confinement field was indeed distorted in our apparatus and it gave rise to the trapped ion to shift from potential center. And the micromotion of r-direction was transferred to the z-axis by the distorted confinement field. The z-axis micromotion was suppressed by increasing cap voltage of trap.

Manipulation of Ions in Microscopic Surface-Electrode Ion Traps

The spatial manipulation of ionic qubits in a fast and precise fashion is one of the foremost issues in scalable quantum information processing with trapped ions. We report our recent efforts toward precise manipulation of trapped ions, including separation, recombination and reordering of the ions, in our home-made microscopic surface-electrode trap. We also demonstrate the micromotion compensation for the trapped ions by rf-photon cross-correlation, which ensures the cooling of the ions down to the temperature 23.3mK.

Detection of ion micromotion in a linear Paul trap with a high finesse cavity

We demonstrate minimization of ion micromotion in a linear Paul trap with the use of a high finesse cavity. The excess ion micromotion projected along the optical cavity axis or along the laser propagation direction manifests itself as sideband peaks around the carrier in the ion-cavity emission spectrum. By minimizing the sideband height in the emission spectrum, we are able to reduce the micromotion amplitude along two directions to approximately the spread of the ground state wave function. This method is useful for cavity QED experiments as it describes the possibility of efficient 3-D micromotion compensation despite optical access limitations imposed by the cavity mirrors. We also show that, in principle, sub-nanometer micromotion compensation is achievable with our current system.

Demonstration of Cold 40Ca+ Ions Confined in a Microscopic Surface-Electrode Ion Trap

40Ca+ ions are successfully confined, under the cooling of a red-detuned laser, in a home-built microscopic surface-electrode (MSE) trap. With all electrodes deposited on a low-rf-loss substrate, our 500-μm-scale MSE trap is designed involving three potential wells and manufactured by the standard technique of the printed circuit board. Both linear and two-dimensional crystals of 40Ca+ are observed in the trap after preliminary micromotion compensation is carried out. The development of the MSE trap aims at large-scale trapped-ion quantum information processing.

Linear ion trap imperfection and the compensation of excess micromotion

Quantum computing requires ultracold ions in a ground vibrational state, which is achieved by sideband cooling. We report our recent efforts towards the Lamb-Dicke regime which is a prerequisite of sideband cooling. We first analyse the possible imperfection in our linear ion trap setup and then demonstrate how to suppress the imperfection by compensating the excess micromotion of the ions. The ions, after the micromotion compensation, are estimated to be very close to the Doppler-cooling limit.

Micromotion compensation in a surface electrode trap by parametric excitation of trapped ions

We report a surface electrode trap with a relatively large trap depth (0.6–1.0 eV). The trap electrodes are formed by gold plating an alumina substrate. Calcium ions are trapped approximately 400 μm above the trap surface. We demonstrate micromotion compensation based on parametric resonance for surface electrode traps. Unlike the conventional method based on radio-frequency (rf)–photon correlation in which the wave vector of the laser beam must have a component parallel to the micromotion to be detected, the proposed method is independent of the laser propagation direction. This enables the micromotion component normal to the electrode surface to be detected without increasing the scattered light.

Micromotion Compensation and Photoionization of Ions in a Linear Trap

The stable confinement of ions in an electromagnetic trap is a prerequisite of sideband cooling and quantum information processing. For a string of ions in a linear ion trap, we report our recent efforts of compensating for micromotion of the ions by three methods, which yields narrower fluorescence spectra and lower temperature. We also achieve a photoionization scheme that loads the ions deterministically into the linear trap from an atomic beam.

Implementation of a symmetric surface-electrode ion trap with field compensation using a modulated Raman effect

We describe a new electrode design for a surface-electrode Paul trap, which allows rotation of the normal modes out of the trap plane, and a technique for micromotion compensation in all directions using a two-photon process, which avoids the need for an ultraviolet laser directed to the trap plane. The fabrication and characterization of the trap are described, as well as its implementation for the trapping and cooling of single Ca+ ions. We also propose a repumping scheme that increases ion fluorescence and simplifies heating rate measurements obtained by time-resolved ion fluorescence during Doppler cooling.

Design and characterization of a planar trap

We demonstrate laser cooling of 40Ca+ ions in a linear-type planar trap where all electrodes are located in a plane. We numerically calculate the potential of a 500 µm scale trap and then characterize the trap by measuring the secular frequencies. Linear crystals of 40Ca+ ions are formed after coarse micromotion compensation. Development of such traps is important for the construction of a many-zone ion-trap array for large-scale quantum information processing using ions. We also present other trap designs and results from numerical analysis.

Controlled photoionization loading of 88Sr+ for precision ion-trap experiments

We report on a photoionization scheme for controlled loading of 88Sr+ ions into a radio-frequency (rf) ion trap. The two-step doubly-resonant process drives the 88Sr atom on the 5s21S0 – 5s5p1P1 transition at 461 nm using a frequency-doubled diode laser, and then excites the atom to the autoionizing (4d2+5p2) 1D2 state with 405 nm light from a free-running diode laser. This method of trap loading is quantitatively compared to electron bombardment loading, and shown to reduce the Sr vapour pressure required to load by four orders of magnitude. It also provides more than an order of magnitude reduction in the day-to-day variation of the voltages required to compensate micromotion. We additionally introduce a two-step atomic source consisting of an oven and hotplate, which reduces the number of impurities evaporated towards the trap. This is shown to significantly reduce fluctuations in required micromotion compensation voltages. The demonstrated reduction in flux and increased source purity are expected to improve the reliability of trap operation for precision ion-trap experiments.