24 research outputs found
Symmetrised Characterisation of Noisy Quantum Processes
A major goal of developing high-precision control of many-body quantum
systems is to realise their potential as quantum computers. Probably the most
significant obstacle in this direction is the problem of "decoherence": the
extreme fragility of quantum systems to environmental noise and other control
limitations. The theory of fault-tolerant quantum error correction has shown
that quantum computation is possible even in the presence of decoherence
provided that the noise affecting the quantum system satisfies certain
well-defined theoretical conditions. However, existing methods for noise
characterisation have become intractable already for the systems that are
controlled in today's labs. In this paper we introduce a technique based on
symmetrisation that enables direct experimental characterisation of key
properties of the decoherence affecting a multi-body quantum system. Our method
reduces the number of experiments required by existing methods from exponential
to polynomial in the number of subsystems. We demonstrate the application of
this technique to the optimisation of control over nuclear spins in the solid
state.Comment: About 12 pages, 5 figure
Photon polarisation entanglement from distant dipole sources
It is commonly believed that photon polarisation entanglement can only be
obtained via pair creation within the same source or via postselective
measurements on photons that overlapped within their coherence time inside a
linear optics setup. In contrast to this, we show here that polarisation
entanglement can also be produced by distant single photon sources in free
space and without the photons ever having to meet, if the detection of a photon
does not reveal its origin -- the which way information. In the case of two
sources, the entanglement arises under the condition of two emissions in
certain spatial directions and leaves the dipoles in a maximally entangled
state.Comment: 7 pages, 2 figures, revised version, accepted for publication in J.
Phys.
Coherence of qubits based on single Ca ions
Two-level ionic systems, where quantum information is encoded in long lived
states (qubits), are discussed extensively for quantum information processing.
We present a collection of measurements which characterize the stability of a
qubit based on the -- transition of single Ca ions
in a linear Paul trap. We find coherence times of 1 ms, discuss the
main technical limitations and outline possible improvements.Comment: Proceedings of "Trapped charged particles and fundamental
interactions" submitted to Journal of Physics B (IoP
Severe neurological outcomes after very early bilateral nephrectomies in patients with autosomal recessive polycystic kidney disease (ARPKD)
To test the association between bilateral nephrectomies in patients with autosomal recessive polycystic kidney disease (ARPKD) and long-term clinical outcome and to identify risk factors for severe outcomes, a dataset comprising 504 patients from the international registry study ARegPKD was analyzed for characteristics and complications of patients with very early (� 3 months; VEBNE) and early (4�15 months; EBNE) bilateral nephrectomies. Patients with very early dialysis (VED, onset � 3 months) without bilateral nephrectomies and patients with total kidney volumes (TKV) comparable to VEBNE infants served as additional control groups. We identified 19 children with VEBNE, 9 with EBNE, 12 with VED and 11 in the TKV control group. VEBNE patients suffered more frequently from severe neurological complications in comparison to all control patients. Very early bilateral nephrectomies and documentation of severe hypotensive episodes were independent risk factors for severe neurological complications. Bilateral nephrectomies within the first 3 months of life are associated with a risk of severe neurological complications later in life. Our data support a very cautious indication of very early bilateral nephrectomies in ARPKD, especially in patients with residual kidney function, and emphasize the importance of avoiding severe hypotensive episodes in this at-risk cohort. © 2020, The Author(s)
Fine analysis of spontaneous MAGE-C1/CT7–specific immunity in melanoma patients
Cancer/testis (CT) antigens represent prime candidates for immunotherapy in cancer patients, because their expression is restricted to cancer cells and germ cells of the testis. MAGE-C1/CT7 is a CT antigen that is highly expressed in several types of cancers. Spontaneous occurrence of CT7-specific antibodies was previously detected by SEREX screen in a melanoma patient. However, naturally occurring CT7-specific T-cell responses have thus far not been detected. Peripheral blood mononuclear cells (PBMCs) from 26 metastatic melanoma patients expressing CT7 in their tumor lesions (CT7+) were analyzed for CT7-specific T-cell responses using overlapping peptides. CT7-specific CD4+ T-cell responses were detected in three patients (11.5%). These CT7-specific CD4+ T-cell responses were detectable in melanoma patients’ PBMCs exclusively from preexisting CD45RA− memory CD4+ T-cell pool. Additional CT7-specific memory CD4+ T-cell responses were detected in CT7+ melanoma patients after depletion of CD4+CD25high Treg cells showing that Treg cells impact on CT7-specific CD4+ T cells in melanoma patients. CT7-specific CD4+ T-cell clones were generated and used to define minimal epitopes, restriction elements, and confirm the recognition of naturally processed antigen. Surprisingly, these clones were able to secrete perforin and exert cytotoxicity. This study shows that CT7 can induce specific cellular immunity in melanoma patients. Based on these findings, CT7 will be further explored as a potential vaccine for melanoma immunotherapy