340 research outputs found
Passive dynamical decoupling of trapped ion qubits and qudits
We propose a method to dynamically decouple every magnetically sensitive
hyperfine sublevel of a trapped ion from magnetic field noise, simultaneously,
using integrated circuits to adiabatically rotate its local quantization field.
These integrated circuits allow passive adjustment of the effective
polarization of any external (control or noise) field. By rotating the ion's
quantization direction relative to this field's polarization, we can perform
`passive' dynamical decoupling (PDD), inverting the linear Zeeman sensitivity
of every hyperfine sublevel. This dynamically decouples the entire ion, rather
than just a qubit subspace. Fundamentally, PDD drives the transition
for every magnetic quantum number in the
system--with only one operation--indicating it applies to qudits with constant
overhead in the dimensionality of the qudit. We show how to perform pulsed and
continuous PDD, weighing each technique's insensitivity to external magnetic
fields versus their sensitivity to diabaticity and control errors. Finally, we
show that we can tune the sinusoidal oscillation of the quantization axis to a
motional mode of the crystal in order to perform a laser-free two qubit gate
that is insensitive to magnetic field noise
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Mixed-species Quantum Logic With Trapped Ions for Gate Teleportation, Metrology, and High-fidelity Indirect Readout
Trapped ions are a leading platform for quantum computation, communication, and metrology, in large part due to their promising pathways to scalability and the high fidelity quantum logic gates enabled by laser and microwave control. We use 9Be+ and 25Mg+ ions to demonstrate how quantum logic operations between separate species of ion can enhance a broad spectrum of quantum technologies. First, we implement quantum gate teleportation between 9Be+ ions in separate potential wells by means of a split entangled pair of 25Mg+ ions, a key primitive for distributing quantum computation across multiple processors or for reducing transport latency in a large segmented trap array. Next, we show how mixed-species multi-ion operations can be used to combine the probe and readout in spectroscopy experiments while providing enhanced sensitivity in the number of spectroscopy ions due to the entangling nature of the operations. Finally, working with two species of ion allows for mid-experiment dissipation to the environment through one species without perturbing the other. This is often used for reinitializing the collective motion to near the ground state, however in the long run the internal ion states will also need to be measured and reinitialized during computation. We therefore propose and demonstrate a protocol for high-fidelity indirect measurement of trapped ion hyperfine qubits that is robust to spontaneous photon scattering and avoids the risk of decohering spectator qubits with stray resonant light.</p
Dissipative preparation of W states in trapped ion systems
We present protocols for dissipative entanglement of three trapped-ion qubits
and discuss a scheme that uses sympathetic cooling as the dissipation
mechanism. This scheme relies on tailored destructive interference to generate
any one of six entangled W states in a three-ion qubit space. Using a
beryllium-magnesium ion crystal as an example system, we theoretically
investigate the protocol's performance and the effects of likely error sources,
including thermal secular motion of the ion crystal, calibration imperfections,
and spontaneous photon scattering. We estimate that a fidelity of 98 %
may be achieved in typical trapped ion experiments with 1 ms interaction
time. These protocols avoid timescale hierarchies for faster preparation of
entangled states
Helping Relationships and Genetic Propensities: A Combinatoric Study of DRD2, Mentoring, and Educational Continuation
Abstract From conception to death, helping relationships promote positive development and enable people to surmount challenges in their lives. Is it the case that the negative consequences of a genetic propensity for risky behaviors can be attenuated by helping relationships (a G × E)? But is it also the case that people with such a genetic propensity are less likely to have helping relationships compared to people without such a propensity (a rGE)? We illustrate this complex pattern of gene–environment interplay by drawing on the National Longitudinal Study of Adolescent Health and a combinatoric analytic strategy. We focus on a gene associated with dopamine receptor type 2 (DRD2 TaqIA), student–mentor relationships, and educational continuation beyond secondary school. Results reveal that, for both white and black males, DRD2 A1+ (A1A1 and A1A2 genotypes) is associated with a decreased likelihood of school continuation compared to their counterparts with DRD2 A1–; mentors who are teachers compensate for this negative association (a G × E); and youth with DRD2 A1+ are less likely to have a mentor who is a teacher than their counterparts with DRD2 A1– (a rGE)
High-fidelity indirect readout of trapped-ion hyperfine qubits
We propose and demonstrate a protocol for high-fidelity indirect readout of
trapped ion hyperfine qubits, where the state of a qubit ion is
mapped to a readout ion using laser-driven Raman
transitions. By partitioning the ground state hyperfine
manifold into two subspaces representing the two qubit states and choosing
appropriate laser parameters, the protocol can be made robust to spontaneous
photon scattering errors on the Raman transitions, enabling repetition for
increased readout fidelity. We demonstrate combined readout and back-action
errors for the two subspaces of and
with 68% confidence while avoiding decoherence
of spectator qubits due to stray resonant light that is inherent to direct
fluorescence detection.Comment: 7 + 6 pages, 3 + 1 figure
Clinical and kidney structural characteristics of living kidney donors with nephrolithiasis and their long-term outcomes
Background: Nephrolithiasis in living kidney donors is concerning due to the potential impact on long-term postdonation kidney function.
Methods: We performed a cohort study of living kidney donors from 2 centers with a baseline computed tomography scan and implantation renal biopsy. Donors (\u3e5 y since donation) completed a follow-up survey or underwent chart review to assess eGFR and incident hypertension. Stone formers were classified as symptomatic if they had a past symptomatic episode or asymptomatic if only incidental radiographic kidney stones were identified during donor evaluation. We compared baseline clinical, imaging, and biopsy characteristics by stone former status including review of metabolic evaluations in stone formers. Long-term risks of renal complications (low eGFR and hypertension) by stone former status were evaluated.
Results: There were 12 symptomatic and 76 asymptomatic stone formers among 866 donors. Overall, baseline clinical characteristics and implantation biopsy findings were similar between stone formers and non-stone formers. After a median follow-up of 10 y, stone former status was not associated with eGFR \u3c60 mL/min/1.73 m2, eGFR \u3c45 mL/min/1.73 m
Conclusions: Both asymptomatic and symptomatic SF have favorable histology findings at baseline. Long-term kidney outcomes were favorable in select stone formers with no evident increased long-term risk for decreased kidney function or hypertension after donation
Magnetic Resonance Guided Radiation Therapy for Pancreatic Adenocarcinoma, Advantages, Challenges, Current Approaches, and Future Directions
Introduction: Pancreatic adenocarcinoma (PAC) has some of the worst treatment outcomes for any solid tumor. PAC creates substantial difficulty for effective treatment with traditional RT delivery strategies primarily secondary to its location and limited visualization using CT. Several of these challenges are uniquely addressed with MR-guided RT. We sought to summarize and place into context the currently available literature on MR-guided RT specifically for PAC.
Methods: A literature search was conducted to identify manuscript publications since September 2014 that specifically used MR-guided RT for the treatment of PAC. Clinical outcomes of these series are summarized, discussed, and placed into the context of the existing pancreatic literature. Multiple international experts were involved to optimally contextualize these publications.
Results: Over 300 manuscripts were reviewed. A total of 6 clinical outcomes publications were identified that have treated patients with PAC using MR guidance. Successes, challenges, and future directions for this technology are evident in these publications. MR-guided RT holds theoretical promise for the treatment of patients with PAC. As with any new technology, immediate or dramatic clinical improvements associated with its use will take time and experience. There remain no prospective trials, currently publications are limited to small retrospective experiences. The current level of evidence for MR guidance in PAC is low and requires significant expansion. Future directions and ongoing studies that are currently open and accruing are identified and reviewed.
Conclusions: The potential promise of MR-guided RT for PAC is highlighted, the challenges associated with this novel therapeutic intervention are also reviewed. Outcomes are very early, and will require continued and long term follow up. MR-guided RT should not be viewed in the same fashion as a novel chemotherapeutic agent for which dosing, administration, and toxicity has been established in earlier phase studies. Instead, it should be viewed as a novel procedural intervention which must be robustly tested, refined and practiced before definitive conclusions on the potential benefits or detriments can be determined. The future of MR-guided RT for PAC is highly promising and the potential implications on PAC are substantial
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