12 research outputs found
Wigner's Friend paradoxes: consistency with weak-contextual and weak-macroscopic realism models
Wigner's friend paradoxes highlight contradictions between measurements made
by Friends inside a laboratory and superobservers outside a laboratory, who
have access to an entangled state of the measurement apparatus. The
contradictions lead to no-go theorems for observer-independent facts, thus
challenging concepts of objectivity. Here, we examine the paradoxes from the
perspective of establishing consistency with macroscopic realism. We present
versions of the Brukner-Wigner-friend and Frauchiger-Renner paradoxes in which
the spin- system measured by the Friends corresponds to two
macroscopically distinct states. The local unitary operations that
determine the measurement setting are carried out using nonlinear
interactions, thereby ensuring measurements need only distinguish between the
macroscopically distinct states. The macroscopic paradoxes are perplexing,
seemingly suggesting there is no objectivity in a macroscopic limit. However,
we demonstrate consistency with a contextual weak form of macroscopic realism
(wMR): The premise wMR asserts that the system can be considered to have a
definite spin outcome , at the time after the system has
undergone the unitary rotation to prepare it in a suitable pointer
basis. We further show that the paradoxical outcomes imply failure of
deterministic macroscopic local realism, and arise when there are unitary
interactions occurring due to a change of measurement setting at
both sites, with respect to the state prepared by each Friend. In models which
validate wMR, there is a breakdown of a subset of the assumptions that
constitute the Bell-Locality premise. A similar interpretation involving a weak
contextual form of realism exists for the original paradoxes
Weak versus deterministic macroscopic realism
We construct a mapping of Bell and bipartite Leggett-Garg experiments for
microscopic qubits onto a gedanken experiment for macroscopic qubits based on
two macroscopically distinct coherent states. This provides an unusual
situation where the dichotomic measurements (and associated hidden variables)
involved in the Bell tests need only discriminate between two macroscopically
distinct states of a system i.e. correspond to coarse-grained measurements that
do not specify values to a level of precision of order . Violations
of macro-realism and macroscopic local realism are predicted. We show how one
may obtain consistency with a weak form of macroscopic realism (wMR): that for
a system prepared in a superposition of macroscopically distinct pointer
eigenstates, the outcome of the coarse-grained pointer measurement is
predetermined. Macroscopic realism does not however hold in a deterministic
fashion, where one assumes the predetermination of outcomes prior to the
unitary rotations that define the choice of measurement setting in the Bell
experiment. We illustrate an analogy with the Einstein-Podolsky-Rosen (EPR)
argument, showing how wMR can be regarded as inconsistent with the completeness
of quantum mechanics
Anti-digoxin Fab fragments in cardiotoxicity induced by ingestion of yellow oleander: a randomised controlled trial.
BACKGROUND: Severe cardiac glycoside cardiotoxicity after ingestion of yellow oleander seeds is an important problem in rural areas of Sri Lanka. Currently, patients must be transferred to the capital for temporary cardiac pacing. We did a randomised controlled trial to investigate whether anti-digoxin Fab could reverse serious oleander-induced arrhythmias. METHODS: After a preliminary dose-finding study, 66 patients who presented to hospital with a serious cardiac arrhythmia were randomised to receive either 1200 mg of anti-digoxin Fab or a saline placebo. A 12-lead electrocardiogram, 3 min rhythm strip, and blood sample for measurement of electrolytes and cardiac glycosides were taken before treatment and at 12 timepoints thereafter. FINDINGS: 34 patients received anti-digoxin Fab and 32 received placebo. The presenting arrhythmia had resolved completely after 2 h in 15 antibody-treated patients and two controls (p<0.001); 24 and five patients, respectively, were in sinus rhythm at 8 h (p<0.001). Kaplan-Meier analysis of time to first reversal showed a significant response to anti-digoxin Fab. The heart rate increased in cases, from 49.1 per min at baseline to 66.8 at 2 h, but not in controls (50.6 per min at baseline to 51.5; p<0.001). Mean serum potassium concentrations decreased from 4.9 mmol/L to 4.1 mmol/L at 2 h in cases; no such decrease occurred in controls. INTERPRETATION: Anti-digoxin Fab fragments are a safe and effective treatment for serious cardiac arrhythmias induced by yellow oleander. Their use in small rural hospitals in Sri Lanka should minimise costly transfer of patients and reduce the numbers of deaths; however, further study will be required to confirm this reduction