Initial Investigation of a Grating Stimulus as a Visual Endpoint for Human Centrifuge Research.

INTRODUCTION: G tolerance has been widely assessed using Peripheral Light Loss (PLL), but this approach has several limitations and may lack sensitivity. The aim of this study was to investigate the use of a foveal visual endpoint for centrifuge research (Grating Loss; GL) and assess its repeatability, reliability, and usability with PLL as a reference.METHODS: A total of 11 subjects undertook centrifuge assessment. Gradual onset sessions (GOR; 0.1 G · s-1) measured both endpoints simultaneously and were performed twice, consisting of six determinations with anti-G suits activated (GOR-On) and six without (GOR-Off). Four determinations of each endpoint were also taken during rapid onset runs (ROR; 3 G · s-1). Usability was scored subjectively.RESULTS: The GL endpoint was reached 0.3-0.5 Gz lower than PLL with each endpoint correlating strongly in GOR-Off (r = 0.93), GOR-On (r = 0.95), and ROR (r = 0.86). The GL had excellent test-retest repeatability (intraclass correlation coefficient: GOR-Off/On = 0.99, ROR = 0.92) and low within-subject variability. Between-subject variance equaled PLL in all conditions. Subjective usability endpoint ratings were equal for all conditions.DISCUSSION: For the 11 individuals tested, the GL was a reliable, repeatable, and usable endpoint, with similar performance to PLL. GL may prove useful as a supplementary endpoint for human centrifuge research as a secondary data point or to reduce fatigue in repeated measurements. The foveal GL stimulus was lost before PLL, contrary to popular models of visual changes under +Gz.Britton J, Connolly DM, Hawarden DE, Stevenson AT, Harridge SDR, Green NDC, Pollock RD. Initial investigation of a grating stimulus as a visual endpoint for human centrifuge research. Aerosp Med Hum Perform. 2023; 94(12):894-901.

Physiological Effects of Centrifuge-Simulated Suborbital Spaceflight.

BACKGROUND: High-G acceleration experienced during launch and re-entry of suborbital spaceflights may present challenges for older or medically susceptible participants. A detailed understanding of the associated physiological responses would support the development of an evidence-based medical approach to commercial suborbital spaceflight.METHODS: There were 24 healthy subjects recruited into 'younger' (18-44 yr), 'intermediate' (45-64 yr) and 'older' (65-80 yr) age groups. Cardiovascular and respiratory variables were measured continuously during dynamic combinations of +Gx (chest-to-back) and +Gz (head-to-foot) acceleration that simulated suborbital G profiles for spaceplane and rocket/capsule platforms. Measurements were conducted breathing air and breathing 15% oxygen to simulate a cabin pressure altitude of 8000 ft.RESULTS: Suborbital G profiles generated highly dynamic changes in heart rate, blood pressure, and cardiac output. G-induced hypoxemia was observed, with minimum arterial oxygen saturation < 80% in a quarter of subjects. Increased age was associated with greater hypoxemia and reduced cardiac output responses but did not have detrimental cardiovascular effects. ECG changes included recurrent G-induced trigeminy in one individual. Respiratory and visual symptoms were common, with 88% of subjects reporting greyout and 29% reporting blackout. There was one episode of G-induced loss of consciousness (G-LOC).DISCUSSION: Suborbital acceleration profiles are generally well tolerated but are not physiologically inconsequential. Marked hemodynamic effects and transient respiratory compromise could interact with predisposing factors to precipitate adverse cardiopulmonary effects in a minority of participants. Medically susceptible individuals may benefit from expanded preflight centrifuge familiarization that includes targeted physiological evaluation in the form of a 'G challenge test'.Smith TG, Pollock RD, Britton JK, Green NDC, Hodkinson PD, Mitchell SJ, Stevenson AT. Physiological effects of centrifuge-simulated suborbital spaceflight. Aerosp Med Hum Perform. 2022; 93(12):830-839.

Cardiac MRI improves cardiovascular risk stratification in hazardous occupations.

BACKGROUND: The benefit of cardiovascular magnetic resonance Imaging (CMR) in assessing occupational risk is unknown. Pilots undergo frequent medical assessment for occult disease, which threatens incapacitation or distraction during flight. ECG and examination anomalies often lead to lengthy restriction, pending full investigation. CMR provides a sensitive, specific assessment of cardiac anatomy, tissue characterisation, perfusion defects and myocardial viability. We sought to determine if CMR, when added to standard care, would alter occupational outcome. METHODS: A retrospective review was conducted of all personnel attending the RAF Aviation Medicine Consultation Service (AMCS) for assessment of a cardiac anomaly, over a 2-year period. Those undergoing standard of care (history, examination, exercise ECG, 24 h-Holter and transthoracic echocardiography), and those undergoing a CMR in addition, were identified. The influence of CMR upon the final decision regarding flying restriction was determined by comparing the diagnosis reached with standard of care plus CMR vs. standard of care alone. RESULTS: Of the ~ 8000 UK military aircrew, 558 personnel were seen for cardiovascular assessment. Fifty-two underwent CMR. A normal TTE did not reliably exclude abnormalities subsequently detected by CMR. Addition of CMR resulted in an upgraded occupational status in 62% of those investigated, with 37% returning to unrestricted duties. Only 8% of referrals were undiagnosed following CMR. All these were cases of borderline chamber dilatation and reduction in systolic function in whom diagnostic uncertainty remained between physiological exercise adaptation and early cardiomyopathy. CONCLUSIONS: CMR increases the likelihood of a definitive diagnosis and of return to flying. This study supports early use of CMR in occupational assessment for high-hazard occupations.

Trapped Ion Quantum Information Processing with Squeezed Phonons.

Trapped ions offer a pristine platform for quantum computation and simulation, but improving their coherence remains a crucial challenge. Here, we propose and analyze a new strategy to enhance the coherent interactions in trapped ion systems via parametric amplification of the ions' motion-by squeezing the collective motional modes (phonons), the spin-spin interactions they mediate can be significantly enhanced. We illustrate the power of this approach by showing how it can enhance collective spin states useful for quantum metrology, and how it can improve the speed and fidelity of two-qubit gates in multi-ion systems, important ingredients for scalable trapped ion quantum computation. Our results are also directly relevant to numerous other physical platforms in which spin interactions are mediated by bosons.

Stroboscopic approach to trapped-ion quantum information processing with squeezed phonons.

In trapped-ion quantum information processing, interactions between spins (qubits) are mediated by collective modes of motion of an ion crystal. While there are many different experimental strategies to design such interactions, they all face both technical and fundamental limitations to the achievable coherent interaction strength. In general, obtaining strong interactions and fast gates is an ongoing challenge. Here, we extend previous work [W. Ge, B. C. Sawyer, J. W. Britton, K. Jacobs, J. J. Bollinger, and M. Foss-Feig, Phys. Rev. Lett. 122, 030501 (2019)] and present a general strategy for enhancing the interaction strengths in trapped-ion systems via parametric amplification of the ions' motion. Specifically, we propose a stroboscopic protocol using alternating applications of parametric amplification and spin-motion coupling. In comparison with the previous work, we show that the current protocol can lead to larger enhancements in the coherent interaction that increase exponentially with the gate time.

Quantum spin dynamics and entanglement generation with hundreds of trapped ions.

Quantum simulation of spin models can provide insight into problems that are difficult or impossible to study with classical computers. Trapped ions are an established platform for quantum simulation, but only systems with fewer than 20 ions have demonstrated quantum correlations. We studied quantum spin dynamics arising from an engineered, homogeneous Ising interaction in a two-dimensional array of (9)Be(+) ions in a Penning trap. We verified entanglement in spin-squeezed states of up to 219 ions, directly observing 4.0 ± 0.9 decibels of spectroscopic enhancement, and observed states with non-Gaussian statistics consistent with oversqueezed states. The good agreement with ab initio theory that includes interactions and decoherence lays the groundwork for simulations of the transverse-field Ising model with variable-range interactions, which are generally intractable with classical methods.

Spectroscopy and thermometry of drumhead modes in a mesoscopic trapped-ion crystal using entanglement.

We demonstrate spectroscopy and thermometry of individual motional modes in a mesoscopic 2D ion array using entanglement-induced decoherence as a method of transduction. Our system is a ~400 µm-diameter planar crystal of several hundred 9Be(+) ions exhibiting complex drumhead modes in the confining potential of a Penning trap. Exploiting precise control over the 9Be(+) valence electron spins, we apply a homogeneous spin-dependent optical dipole force to excite arbitrary transverse modes with an effective wavelength approaching the interparticle spacing (~20 µm). Center-of-mass displacements below 1 nm are detected via the entanglement of spin and motional degrees of freedom.

Engineered two-dimensional Ising interactions in a trapped-ion quantum simulator with hundreds of spins.

The presence of long-range quantum spin correlations underlies a variety of physical phenomena in condensed-matter systems, potentially including high-temperature superconductivity. However, many properties of exotic, strongly correlated spin systems, such as spin liquids, have proved difficult to study, in part because calculations involving N-body entanglement become intractable for as few as N ≈ 30 particles. Feynman predicted that a quantum simulator--a special-purpose 'analogue' processor built using quantum bits (qubits)--would be inherently suited to solving such problems. In the context of quantum magnetism, a number of experiments have demonstrated the feasibility of this approach, but simulations allowing controlled, tunable interactions between spins localized on two- or three-dimensional lattices of more than a few tens of qubits have yet to be demonstrated, in part because of the technical challenge of realizing large-scale qubit arrays. Here we demonstrate a variable-range Ising-type spin-spin interaction, J(i,j), on a naturally occurring, two-dimensional triangular crystal lattice of hundreds of spin-half particles (beryllium ions stored in a Penning trap). This is a computationally relevant scale more than an order of magnitude larger than previous experiments. We show that a spin-dependent optical dipole force can produce an antiferromagnetic interaction J(i,j) proportional variant d(-a)(i,j), where 0 ≤ a ≤ 3 and d(i,j) is the distance between spin pairs. These power laws correspond physically to infinite-range (a = 0), Coulomb-like (a = 1), monopole-dipole (a = 2) and dipole-dipole (a = 3) couplings. Experimentally, we demonstrate excellent agreement with a theory for 0.05 ≲ a ≲ 1.4. This demonstration, coupled with the high spin count, excellent quantum control and low technical complexity of the Penning trap, brings within reach the simulation of otherwise computationally intractable problems in quantum magnetism.