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arXiv:2108.06948 · Quantum Science and Technology

A deterministic single ion fountain

Felix Stopp, Henri Lehec, Ferdinand Schmidt‐Kaler

Published Mar 21, 2022• 3 citations
arXivHTMLPDF

Abstract

Abstract We present an alternative approach for interconnecting trapped ion processor nodes by deterministic single ion transfer. In our experiments, we demonstrate the single ion extraction out of a linear Paul trap, into a free space trajectory, followed by recapture in the trapping potential. We recapture in the same trap, coined the ion fountain operation after a free-space travel of distance 110 mm and a time of flight of 7 μ s. Our experimental realization yields a success probability of 95.1%, namely 715 out of 752 extracted ions are retrapped, cooled and observed. Based on such high success rate, we discuss the future perspective for an application towards scalable ion trap quantum computing and advanced quantum sensing.

DOI
10.1088/2058-9565/ac5f5c

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Abstract We present an alternative approach for interconnecting trapped ion processor nodes by deterministic single ion transfer. In our experiments, we demonstrate the single ion extraction out of a linear Paul trap, into a free space trajectory, followed by recapture in the trapping potential. We recapture in the same trap, coined the ion fountain operation after a free-space travel of distance 110 mm and a time of flight of 7 μ s. Our experimental realization yields a success probability of 95.1%, namely 715 out of 752 extracted ions are retrapped, cooled and observed. Based on such high success rate, we discuss the future perspective for an application towards scalable ion trap quantum computing and advanced quantum sensing.
Summary form only given. We discuss experiments with trapped /sup 9/Be/sup +/ ions in a micro-machined linear Paul trap that has two trapping regions separated by 1.2 mm. This trap geometry permits experiments that are the first steps toward a multiplexed, scalable quantum computer. We demonstrate coherent manipulations on a single ion that is transported between trapping regions, separation of two ions, and a quantum logic gate on a single ion that is made possible by the significantly reduced heating rate in this trap. We demonstrate adiabatic transport of a single ion between the trapping regions using time varying electrode potentials. A single ion is transported adiabatically over 1.2 mm between the trapping regions in 500 /spl mu/s with a measured increase of 0.1 /spl plusmn/ 0.1 motional quanta. A single ion has been transported between traps non-adiabatically in times as short as 50 /spl mu/s. Through manipulation of the electrode potentials we also show controlled separation of two ions initially held in one region to two regions that are separated by 1.2 mm.
Abstract A single 40Ca ion is confined in the harmonic potential of a Paul trap and cooled to a temperature of a few mK, with a wave packet of sub-μm spatial and sub-m s−1 velocity uncertainty. Deterministically extracted from the Paul trap, the single ion is propagating over a distance of 0.27 m and detected. By engineering the ion extraction process on the initial wave packet, theoretically modeling the ion trajectories, and studying experimentally the time-of-flight distribution, we directly infer the state of the previously trapped ion. This analysis allows for accurate remote sensing of the previous motional excitation in the trap potential, both coherently or incoherently. Our method paves a way to extract, manipulate and design quantum wave packets also outside of the Paul trap.
Using a segmented ion trap with mK laser-cooled ions we have realised a novel single ion source which can deterministically deliver a wide range of ion species, isotopes or ionic molecules [Schnitzler et al. Phys. Rev. Lett. 2009, 102, 070501]. Experimental data is discussed in detail and compared with numerical simulations of ion trajectories. For the novel ion source we numerically investigate the influence of various extraction parameters on fluctuations in velocity and position of the beam. We present specialised ion optics and show from numerical simulations that a nm spatial resolution is achievable. The Paul trap, which is used as a single ion source, together with the presented ion optics, constitutes a promising candidate for a deterministic ion implantation method for applications in solid state quantum computing or classical nano-electronic devices.
We report on a deterministic single ion source with high repetition rate and high fidelity. The source employs a magneto-optical trap, where ultracold rubidium atoms are photoionized. The electrons herald the creation of a corresponding ion, whose timing information is used to manipulate its trajectory in flight. We demonstrate an ion rate of up to and achieve a fidelity for single ion operation of 98%. The technique can be used for all atomic species, which can be laser-cooled, and opens up new applications in ion microscopy, ion implantation and surface spectroscopy.
Trapped ion systems are the leading candidate for quantum information processing because many of the critical components have already been demonstrated. Scaling trapped ion systems to large numbers of ions is currently believed possible, but much work remains to prove it. Microfabricated surface ion traps are increasing in popularity for their ease of mass production and their ability to manipulate individual ions and interact arbitrary pairs of ions. Even with the advent of scalable ion traps, detection of an individual ion trapped in a high vacuum poses a challenge. The internal state of the ion chosen for a quantum bit can be measured via exposure to a probe beam that causes one state to scatter light (a "bright" state), but not the other state (a "dark" state). In free space, a single ion acts like a point source that emits in all directions; a standard two inch lens system can only collect about 2% of the light emitted by the ion. Poor light collection results in a high error rate and slow determination of the internal state of the ion. Fast, high fidelity state detection is necessary for quantum error correction and loophole-free Bell experiments at short (less than 100\\,km) distances, and high efficiency collection is necessary to rapidly interconnect separate quantum computers. We demonstrate state detection fidelities of 99%, 99.856(8)% and 99.915(7) % which correspond to detection times of 10.5, 28.1 and 99.8 us, respectively.
All of the essential elements for a trapped ion quantum computer have been demonstrated in previous experiments. There are, however, many technical challenges to scaling the number of quantum bits from the current state-of-the-art (about 8) to the number of qubits needed for practical quantum computing. Although there is experimental evidence supporting one possible method (using cw laser pulses and common motional modes as the ion interaction) for deterministic ion entanglement, it is not known if that will ultimately be the most practical method for building a large-scale quantum computer. One model for scalable quantum computing with trapped ions calls for large interconnected arrays of small traps. Several advancements reported in this work include the development of three layer alumina traps as well as MEMS fabricated microtraps. Other models for scalable trapped ion quantum computing do not call for local entanglement or call for relaxed constraints on the motional control of the ions. These proposals require the use of ultrafast laser pulses interacting with the ions. This work reviews several experiments that explore the interaction between the ultrafast laser and single tripped ions including early indication of ultrafast control and entanglement between a single ion and a single photon frequency qubit.