David J. Wineland’s research while affiliated with University of Oregon and other places

Ba+133 is illuminated by a laser that is far detuned from optical transitions, and the resulting spontaneous Raman scattering rate is measured. The observed scattering rate is lower than previous theoretical estimates. The majority of the discrepancy is explained by a more accurate treatment of the scattered photon density of states. This work establishes that, contrary to previous models, there is no fundamental atomic physics limit to laser-driven quantum gates from laser-induced spontaneous Raman scattering.

{}^{133}\mathrm{Ba}^+$ is illuminated by a laser that is far-detuned from optical transitions, and the resulting spontaneous Raman scattering rate is measured. The observed scattering rate is lower than previous theoretical estimates. The majority of the discrepancy is explained by a more accurate treatment of the scattered photon density of states. This work establishes that, contrary to previous models, there is no fundamental limit to laser-driven quantum gates from laser-induced spontaneous Raman scattering.

Scaling quantum information processors is a challenging task, requiring manipulation of a large number of qubits with high fidelity and a high degree of connectivity. For trapped ions, this can be realized in a 2D array of interconnected traps in which ions are separated, transported, and recombined to carry out quantum operations on small subsets of ions. Here, functionality of a junction connecting orthogonal linear segments in a 2D trap array to reorder a two‐ion crystal is demonstrated. The secular motion of the ions experiences low energy gain and the internal qubit levels maintain coherence during the reordering process, therefore demonstrating a promising method for providing all‐to‐all connectivity in a large‐scale, 2D or 3D trapped‐ion quantum information processor.

Special quantum states are used in metrology to achieve sensitivities below the limits established by classically behaving states1,2. In bosonic interferometers, squeezed states3, number states4,5 and 'Schrödinger cat' states5 have been implemented on various platforms and have demonstrated improved measurement precision over interferometers using coherent states6,7. Another metrologically useful state is an equal superposition of two eigenstates with maximally different energies; this state ideally reaches the full interferometric sensitivity allowed by quantum mechanics8,9. Here we demonstrate the enhanced sensitivity of these quantum states in the case of a harmonic oscillator. We extend an existing experimental technique10 to create number states of order up to n = 100 and to generate superpositions of a harmonic oscillator ground state and a number state of the form [Formula: see text] with n up to 18 in the motion of a single trapped ion. Although experimental imperfections prevent us from reaching the ideal Heisenberg limit, we observe enhanced sensitivity to changes in the frequency of the mechanical oscillator. This sensitivity initially increases linearly with n and reaches a maximum at n = 12, where we observe a metrological enhancement of 6.4(4) decibels (the uncertainty is one standard deviation of the mean) compared to an ideal measurement on a coherent state with the same average occupation number. Such measurements should provide improved characterization of motional decoherence, which is an important source of error in quantum information processing with trapped ions11,12. It should also be possible to use the quantum advantage from number-state superpositions to achieve precision measurements in other harmonic oscillator systems.

Teleporting a trapped-ion quantum gate Gating—controlling the state of one qubit conditioned on the state of another—is a key procedure in all quantum information processors. As the scale of quantum processors increases, the qubits will need to interact over larger and larger distances, which presents an experimental challenge in solid-state architectures. Wan et al. implemented the 20-year-old theoretical proposal of quantum gate teleportation that allows separated qubits to interact effectively. They deterministically teleported a controlled-NOT gate between two computational qubits in spatially separated zones in a segmented ion trap, demonstrating a feasible route toward scalable quantum information processors. Science , this issue p. 875

Coherently displaced number states of a harmonically bound ion can be coupled to two internal states of the ion by a laser-induced motional sideband interaction. The internal states can subsequently be read out in a projective measurement via state-dependent fluorescence, with near-unit fidelity. This leads to a rich set of line shapes when recording the internal-state excitation probability after a sideband excitation, as a function of the frequency detuning of the displacement drive with respect to the ion’s motional frequency. We precisely characterize the coherent displacement based on the resulting line shapes, which exhibit sharp features that are useful for oscillator frequency determination from the single quantum regime up to very large coherent states with average occupation numbers of several hundred. We also introduce a technique based on multiple coherent displacements and free precession for characterizing noise on the trapping potential in the frequency range of 500 Hz–400 kHz. Signals from the ion are directly used to find and eliminate sources of technical noise in this typically unaccessed part of the spectrum.

Large-scale quantum computers will inevitably require quantum gate operations between widely separated qubits, even within a single quantum information processing device. Nearly two decades ago, Gottesman and Chuang proposed a method for implementing such operations, known as quantum gate teleportation (1). It requires only local operations on the remote qubits, classical communication, and shared entanglement that is prepared before the logical operation. Here we demonstrate this approach in a scalable architecture by deterministically teleporting a controlled-NOT (CNOT) gate between two computational qubits in spatially separated zones in a segmented ion trap. Our teleported CNOT's entanglement fidelity is in the interval [0.845, 0.872] at the 95% confidence level. The implementation combines ion shuttling with individually-addressed single-qubit rotations and detections, same- and mixed-species two-qubit gates, and real-time conditional operations, thereby demonstrating essential tools for scaling trapped-ion quantum computers combined in a single device.

Coherently displaced harmonic oscillator number states of a harmonically bound ion can be coupled to two internal states of the ion by a laser-induced motional sideband interaction. The internal states can subsequently be read out in a projective measurement via state-dependent fluorescence, with near-unit fidelity. This leads to a rich set of line shapes when recording the internal-state excitation probability after a sideband excitation, as a function of the frequency detuning of the displacement drive with respect to the ion's motional frequency. We precisely characterize the coherent displacement based on the resulting line shapes, which exhibit sharp features that are useful for oscillator frequency determination from the single quantum regime up to very large coherent states with average occupation numbers of several hundred. We also introduce a technique based on multiple coherent displacements and free precession for characterizing noise on the trapping potential in the frequency range of 500 Hz to 400 kHz. Signals from the ion are directly used to find and eliminate sources of technical noise in this typically unaccessed part of the spectrum.

The use of special quantum states in boson interferometry to achieve sensitivities below the limits established by classically-behaving coherent states has enjoyed immense success since its inception. Squeezed states, number states and cat states have been implemented on various platforms and have demonstrated improved measurement precision over coherent-state-based interferometers. Another state is an equal superposition of two eigenstates with maximally different energies; this state ideally reaches the full interferometric sensitivity allowed by quantum mechanics. We extend a technique to create number states up to n = 100 and to generate superpositions of a harmonic oscillator ground state and a number state of the form $1/\sqrt{2}(|0\rangle+|n\rangle)$ up to n = 18 in the motion of a single trapped ion. While experimental imperfections prevent us from reaching the ideal Heisenberg limit, we observe enhanced sensitivity to changes in the oscillator frequency that initially increases linearly with n, with maximal value at n = 12 where we observe 2.1(1) times higher sensitivity compared to an ideal measurement on a coherent state with the same average occupation number. The quantum advantage from using number-state superpositions can be leveraged towards precision measurements on any harmonic oscillator system; here it enables us to track the average fractional frequency of oscillation of a single trapped ion to approximately $2.6 \times 10^{-6}$ in 5 s. Such measurements should enable improved characterization of imperfections and noise on trapping potentials, which can lead to motional decoherence, an important source of error in quantum information processing with trapped ions.