Robust entanglement by continuous dynamical decoupling of the J-coupling interaction

We propose a σz⊗ σzlaser-free entangling gate which uses the intrinsic J-coupling of ions in a static magnetic gradient. Dephasing of the interaction is suppressed by means of continuous dynamical decoupling using pairs of microwave fields. The gate is virtually insensitive to common amplitude noise of the microwave fields and enables high fidelities despite qubit frequency fluctuations, while the J-coupling interaction's inherent robustness to motional decoherence is retained. Errors far below the fault-tolerant threshold can be achieved at high initial temperatures, negating the requirement of sideband cooling below the Doppler temperature. By adjusting the powers of the continuous microwave fields, the J-coupling interaction can be tuned and can be used to implement parallel entangling gates within an ion chain

Robust and Deterministic Preparation of Bosonic Logical States in a Trapped Ion

Encoding logical qubits in bosonic modes provides a potentially hardware-efficient implementation of fault-tolerant quantum information processing. Recent advancements in trapped ions and superconducting microwave cavities have led to experimental realizations of high-quality bosonic states and demonstrations of error-corrected logical qubits encoded in bosonic modes. However, current protocols for preparing bosonic code words lack robustness to common noise sources and can be experimentally challenging to implement, limiting the quality and breadth of codes that have been realized to date. Here, we combine concepts of error suppression via robust control with quantum error correction encoding and experimentally demonstrate high-fidelity, deterministic preparation of highly non-classical target bosonic states in the mechanical motion of a trapped ion. Our approach implements numerically optimized dynamical modulation of laser-driven spin-motion interactions to generate the target state in a single step. The optimized control pulses are tailored towards experimental constraints and are designed to be robust against the dominant source of error. Using these protocols, we demonstrate logical fidelities for the Gottesman-Kitaev-Preskill (GKP) state as high as $\bar{\mathcal{F}}=0.940(8)$, achieve the first realization of a distance-3 binomial logical state with an average fidelity of $\mathcal{F}=0.807(7)$, and demonstrate a 12.91(5) dB squeezed vacuum state.Comment: 12 pages, 8 figure

Culpability for Violence in the Congo: Lessons from the Crisis of 1960–1965

During Congo’s emergence from colonization in the mid-twentieth century, coups, political assassinations, and ethnic massacres took place that exacerbated inequality and insecurity in the region then and ever since. Some Western literature has essentialized these events, implying that they were a product of African people’s innate disorganization, divisiveness, leftism, and violence. Many of the writings keep to surface appearances rather than probing behind-the-scenes causalities. Evidence from archives, images, memoirs, and interviews, however, reveals a counterintuitive complexity in both the representation and perpetration of the direct and structural violence of the Congo crisis. Very different cultures, financing, technology, and interactions were characteristic of the western state agents who sponsored, organized, took part in, and often wrote about the coups and killings in Congo as opposed to the African functionaries with whom and against whom they worked. This chapter illustrates some of the evidence for these complex and contrasting patterns, offers alternative explanations, and outlines some lessons to be learned from the crisis