Abstract Experimental implementations of quantum simulation must balance control‐field‐induced decoherence with the controllability of the quantum system. The ratio of coherent interaction strength to decoherence induced by stimulated emission in atomic systems is typically determined by hardware constraints, limiting the flexibility needed to explore different operating regimes. Here, an optomechanical system is presented for in situ tuning of the coherent spin‐motion and spin‐spin interaction strength in 2D ion crystals in a Penning trap. Enabled by precision closed‐loop piezo‐actuated positioners integrated into the confined space of a superconducting magnet's bore, the system allows tuning of the angle‐of‐incidence of Raman laser beams up to , governing the ratio of coherent to incoherent light‐matter interaction for fixed optical power. System characterization involves measurements of the induced mean‐field spin precession under the application of an optical dipole force in ion crystals cooled below the Doppler limit through electromagnetically induced transparency cooling. These experiments show approximately a variation in the coherent to incoherent interaction ratio with changing , consistent with theoretical predictions. The system stability is characterized over 6000 s, resulting in a drift rate of h –1 . These technical developments will be crucial in future quantum simulations and sensing applications.
Abstract Experimental implementations of quantum simulation must balance control‐field‐induced decoherence with the controllability of the quantum system. The ratio of coherent interaction strength to decoherence induced by stimulated emission in atomic systems is typically determined by hardware constraints, limiting the flexibility needed to explore different operating regimes. Here, an optomechanical system is presented for in situ tuning of the coherent spin‐motion and spin‐spin interaction strength in 2D ion crystals in a Penning trap. Enabled by precision closed‐loop piezo‐actuated positioners integrated into the confined space of a superconducting magnet's bore, the system allows tuning of the angle‐of‐incidence of Raman laser beams up to , governing the ratio of coherent to incoherent light‐matter interaction for fixed optical power. System characterization involves measurements of the induced mean‐field spin precession under the application of an optical dipole force in ion crystals cooled below the Doppler limit through electromagnetically induced transparency cooling. These experiments show approximately a variation in the coherent to incoherent interaction ratio with changing , consistent with theoretical predictions. The system stability is characterized over 6000 s, resulting in a drift rate of h –1 . These technical developments will be crucial in future quantum simulations and sensing applications.
We present the design, construction, and characterization of an experimental system capable of supporting a broad class of quantum simulation experiments with hundreds of spin qubits using 9Be+ ions in a Penning trap. This article provides a detailed overview of the core optical and trapping subsystems and their integration. We begin with a description of a dual-trap design separating loading and experimental zones and associated vacuum infrastructure design. The experimental-zone trap electrodes are designed for wide-angle optical access (e.g., for lasers used to engineer spin-motional coupling across large ion crystals) while simultaneously providing a harmonic trapping potential. We describe a near-zero-loss liquid-cryogen-based superconducting magnet, employed in both trapping and establishing a quantization field for ion spin-states and equipped with a dual-stage remote-motor LN2/LHe recondenser. Experimental measurements using a nuclear magnetic resonance (NMR) probe demonstrate part-per-million homogeneity over 7 mm-diameter cylindrical volume, with no discernible effect on the measured NMR linewidth from pulse-tube operation. Next, we describe a custom-engineered inbore optomechanical system which delivers ultraviolet (UV) laser light to the trap and supports multiple aligned optical objectives for topview and sideview imaging in the experimental trap region. We describe design choices including the use of nonmagnetic goniometers and translation stages for precision alignment. Furthermore, the optomechanical system integrates UV-compatible fiber optics which decouple the system’s alignment from remote light sources. Using this system, we present site-resolved images of ion crystals and demonstrate the ability to realize both planar and three-dimensional ion arrays via control of rotating wall electrodes and radial laser beams. Looking to future work, we include interferometric vibration measurements demonstrating root-mean-square trap motion of ∼33 nm (∼117 nm) in the axial (transverse) direction; both values can be reduced when operating the magnet in free-running mode. The paper concludes with an outlook toward extensions of the experimental setup, areas for improvement, and future experimental studies.
In the search for new computational paradigms past the impending end of Moore’s law quantum information processing based on cold trapped ions has emerged as a promising candidate. This thesis presents on the design, construction and testing of a setup for analog quantum simulation experiments using Be ion crystals in a Penning trap. At the heart of the experiment is a specialized Penning trap with wide optical access for engineering Ising-type interactions. The trap sits inside a superconducting magnet which runs continuously with minimal losses through a novel dual-stage reliquefier system. During this thesis, mechanical and optical subsystems for this ion trap quantum simulator were designed and built. Two laser systems based on nonlinear frequency conversion were set up to generate light for photoionization, Doppler cooling, state preparation, readout, and Raman interactions. In parallel, a method was devised to produce ultraviolet-solarization resistant fiber patch cords for pointing-stable light delivery. Inbore optomechanics and a collaboratively designed precision six-axis positioning device were constructed for beam delivery and trap alignment, respectively. These optomechanics co-locate custom-designed millimeterwave delivery systems as well as numerically optimized, diffraction-limited imaging optics for fluorescence readout. Using these subsystems, we validate interferometrically the motional stability of the setup from the mHz to kHz region during pulse-tube operation. First-ever light-ion interaction serves to validate calculations of interaction frequencies, optomechanics operation, and imaging performance, while coherent qubit interaction allows for this to be done on the millimeter wave setup, where initial Rabi flopping times of 18 us were observed. Site-resolved imaging of rapidly rotating ion crystals demonstrates critical phase-locked operation of the apparatus; positioning the experiment for future upgrades towards a full analog quantum simulator.
Quantum simulations using AMO systems promise a new way to experimentally study emergent quantum phenomena, but few systems have demonstrated the capability to control ensembles in which quantum effects cannot be directly computed. The 2D array of 100s of 9Be+ ions in a Penning trap, crystallized in a triangular lattice when laser cooled, is a promising platform for intractable quantum simulations using the 9Be+ valence electron spin as a qubit [1]. Spin-dependent forces are employed to modify the strong Coulomb interaction of the ions, mimicking a quantum magnetic interaction. The range of the magnetic interaction can be tuned from infinite to a dipole-dipole like coupling. Combining the application of the spin-dependent force with a transverse magnetic field should lead to the development of quantum correlations between the spins, which can be measured through optical readout of the spin state, both globally and with site-resolved imaging. In this way, trapped atomic ions can be used to probe novel and intractable aspects of quantum magnetism, including the effects of long-range interactions and simulations of quantum non-equilibrium phenomena [2]. In addition to a general overview, I will discuss recent work from a new Penning trap set-up at NIST.
From subatomic particles to macromolecules, quantum mechanics has a deep impact in understanding the interactions and nature of such constituents of matter. The paradoxical observations of entanglement in quantum systems is used in quantum computations. Ion traps are among the leading platforms which provide clean and highly controllable quantum systems. This thesis presents the study of quantum coherence aiming to devise and test coherent control with trapped ions in a Penning trap. Our apparatus contains one or more calcium ions that are confined in space using DC electric and magnetic fields. Doppler cooling and resolved sideband cooling of trapped ions are carried out to perform high fidelity quantum control. The ions are prepared in their motional ground state via a multi-stage resolved sideband cooling technique. The cooling methods are first verified through simulations. The axial mean phonon numbers for a single ion are measured to be 0.03 ± 0.01 and 0.012 ± 0.009 at 187 kHz and 420 kHz axial frequencies, respectively. The heating rate is measured to be 2.5 ± 0.5 phonons/s, which is consistent with the previous measurements in our system. Similarly, the radial motional modes of a single ion are cooled to 〈n_+ 〉<0.4 and 〈n_- 〉<0.6 from mean phonon numbers corresponding to each mode of around 100. Preliminary studies are carried out of the axial motional modes of a 1D chain and 2D planar crystals, extending sideband cooling to small ICC's in a Penning trap. Coherent control is examined in our system and the optical coherence time and motional coherence time are estimated to be approximately 1 ms and 0.5 s, respectively. Furthermore, a single ion is prepared outside the Lamb-Dicke regime via a sideband heating technique and coherent studies are performed in such a regime via a laser beam.
Large ion crystals in Penning traps provide a platform for quantum simulation and sensing with hundreds of spins, but their continuous rigid-body rotation has so far limited flexible local qubit control. Here we demonstrate programmable coherent site-selective spin control across large rotating 9Be+ crystals in a Penning trap. A tightly focused off-resonant laser beam drives local Rz phase rotations via differential AC Stark shifts. Beam steering synchronised with crystal rotation enables addressing of arbitrary ions throughout the crystal. Ramsey-based characterisation shows Rz(π) gate fidelity of 0.950(4) and nearest-neighbour crosstalk error of 0.021(6). We demonstrate preparing spatially structured spin patterns, generating a biskyrmion spin texture in a single-layer crystal, and then extend the method to bilayer crystals where we perform layer-selective addressing operations. We further demonstrate dual-quadrature Ramsey sensing by imprinting a relative π/2 phase shift between spatial sub-ensembles, enabling simultaneous measurement of orthogonal spin components within a single experimental realisation. These results establish programmable local control in large rotating ion crystals, opening new routes for engineering spatially structured quantum states in multidimensional trapped-ion systems.
Improving coherence is a fundamental challenge in quantum simulation and sensing experiments with trapped ions. Here we discuss, experimentally demonstrate, and estimate the potential impacts of two different protocols that enhance, through motional parametric excitation, the coherent spin-motion coupling of ions obtained with a spin-dependent force. The experiments are performed on two-dimensional crystal arrays of approximately 100 9Be+ ions confined in a Penning trap. By modulating the trapping potential at close to twice the center-of-mass mode frequency, we squeeze the motional mode and enhance the spin-motion coupling while maintaining spin coherence. With a stroboscopic protocol, we measure $5.4\ifmmode\pm\else\textpm\fi{}0.9\phantom{\rule{0.28em}{0ex}}\mathrm{dB}$ of motional squeezing below the ground-state motion, from which theory predicts a 10-dB enhancement in the sensitivity for measuring small displacements using a recently demonstrated protocol [K. A. Gilmore et al., Science 373, 673 (2021)]. With a continuous squeezing protocol, we measure and accurately calibrate the parametric coupling strength. Theory suggests this protocol can be used to improve quantum spin squeezing, limited in our system by off-resonant light scatter. We illustrate numerically the trade-offs between strong parametric amplification and motional dephasing in the form of center-of-mass frequency fluctuations for improving quantum spin squeezing in our setup.