Significant loophole-free test of Kochen-Specker contextuality using two species of atomic ions

Quantum measurements cannot be thought of as revealing preexisting results, even when they do not disturb any other measurement in the same trial. This feature is called contextuality and is crucial for the quantum advantage in computing. Here, we report the observation of quantum contextuality simultaneously free of the detection, sharpness, and compatibility loopholes. The detection and sharpness loopholes are closed by adopting a hybrid two-ion system and highly efficient fluorescence measurements offering a detection efficiency of 100% and a measurement repeatability of >98%. The compatibility loophole is closed by targeting correlations between observables for two different ions in a Paul trap, a ¹⁷¹Yb⁺ ion and a ¹³⁸Ba⁺ ion, chosen so measurements on each ion use different operation laser wavelengths, fluorescence wavelengths, and detectors. The experimental results show a violation of the bound for the most adversarial noncontextual models and open a way to certify quantum systems.

Single ion qubit with estimated coherence time exceeding one hour

Realizing a long coherence time quantum memory is a major challenge of current quantum technology. Until now, the longest coherence-time of a single qubit was reported as 660 s in a single 171Yb+ ion-qubit through the technical developments of sympathetic cooling and dynamical decoupling pulses, which addressed heating-induced detection inefficiency and magnetic field fluctuations. However, it was not clear what prohibited further enhancement. Here, we identify and suppress the limiting factors, which are the remaining magnetic-field fluctuations, frequency instability and leakage of the microwave reference-oscillator. Then, we observe the coherence time of around 5500 s for the 171Yb+ ion-qubit, which is the time constant of the exponential decay fit from the measurements up to 960 s. We also systematically study the decoherence process of the quantum memory by using quantum process tomography and analyze the results by applying recently developed resource theories of quantum memory and coherence. Our experimental demonstration will accelerate practical applications of quantum memories for various quantum information processing, especially in the noisy-intermediate-scale quantum regime.

NOON States of Nine Quantized Vibrations in Two Radial Modes of a Trapped Ion

We develop a deterministic method to generate and verify arbitrarily high NOON states of quantized vibrations (phonons), through the coupling to the internal state. We experimentally create the entangled states up to N=9 phonons in two vibrational modes of a single trapped ^{171}Yb^{+} ion. We observe an increasing phase sensitivity of the generated NOON state as the number of phonons N increases and obtain the fidelity from the contrast of the phase interference and the population of the phonon states through the two-mode projective measurement, which are significantly above the classical bound. We also measure the quantum Fisher information of the generated state and observe Heisenberg scaling in the lower bounds of phase sensitivity as N increases. Our scheme is generic and applicable to other photonic or phononic systems such as circuit QED systems or nanomechanical oscillators, which have Jaynes-Cummings-type of interactions.

Testing nonclassicality and non-gaussianity in phase space

We theoretically propose and experimentally demonstrate a nonclassicality test of a single-mode field in phase space, which has an analogy with the nonlocality test proposed by Banaszek and Wódkiewicz [Phys. Rev. Lett. 82, 2009 (1999)]. Our approach to deriving the classical bound draws on the fact that the Wigner function of a coherent state is a product of two independent distributions as if the orthogonal quadratures (position and momentum) in phase space behave as local realistic variables. Our method detects every pure nonclassical Gaussian state, which can also be extended to mixed states. Furthermore, it sets a bound for all Gaussian states and their mixtures, thereby providing a criterion to detect a genuine quantum non-Gaussian state. Remarkably, our phase-space approach with invariance under Gaussian unitary operations leads to an optimized test for a given non-Gaussian state. We experimentally show how this enhanced method can manifest quantum non-Gaussianity of a state by simply choosing phase-space points appropriately, which is essentially equivalent to implementing a squeezing operation on a given state.

State-independent experimental test of quantum contextuality with a single trapped ion

Using a single trapped ion, we have experimentally demonstrated state-independent violation of a recent version of the Kochen-Specker inequality in a three-level system (qutrit) that is intrinsically indivisible. Three ground states of the (171)Yb(+) ion representing a qutrit are manipulated with high fidelity through microwaves and detected with high efficiency through a two-step quantum jump technique. Qutrits constitute the most fundamental system to show quantum contextuality and our experiment represents the first one that closes the detection efficiency loophole for experimental tests of quantum contextuality in such a system.

Protective effects of Glycyrrhiza uralensis Fisch. on the cognitive deficits caused by beta-amyloid peptide 25-35 in young mice

Amyloid beta protein (Abeta) may be involved in the progression of Alzheimer's disease (AD), by acting as a neurotoxin and eliciting oxidative stress. This study was designed to determine the effects of Glycyrrhiza uralensis Fisch. water extract (GWE) on the cognitive deficits and oxidative stress induced by the administration of Abeta(25-35) in mice. Mice in two of the four animal groups were fed an experimental diet containing either 0.5 or 1% GWE for the entire 6-week experimental period. Control mice and a further experimental group were fed a non-GWE diet. Abeta(25-35) was administered to the three experimental groups by intracerebroventricular (i.c.v.) injection (10 microg/10 microl/mouse) once per week in weeks 5 and 6 of the experimental period. Behavioral changes were assessed using both a passive avoidance (after the injection of Abeta(25-35) in week 5) and the Morris water-maze tests (after the injection of Abeta(25-35) in week 6). Control animals were administered vehicle alone. The prolonged consumption of a diet containing GWE ameliorated the cognitive deficits caused by the i.c.v. injections of Abeta(25-35). Treatment with Abeta(25-35) led to higher concentrations of thiobarbituric acid reactive substances in the brain, and GWE attenuated this response. There was a decrease in catalase activity in the group provided with 1% GWE. Acetylcholinesterase activity was significantly reduced in the brains of all GWE-treated animals compared to that in the non-GWE-fed experimental group. These results suggest that GWE exerts a protective effect against the cognitive impairments often observed in AD, and that in mice this effect is mediated by antioxidant actions against oxidative stress.

Heterozygous disruption of the TATA-binding protein gene in DT40 cells causes reduced cdc25B phosphatase expression and delayed mitosis

TATA-binding protein (TBP) is a key general transcription factor required for transcription by all three nuclear RNA polymerases. Although it has been intensively analyzed in vitro and in Saccharomyces cerevisiae, in vivo studies of vertebrate TBP have been limited. We applied gene-targeting techniques using chicken DT40 cells to generate heterozygous cells with one copy of the TBP gene disrupted. Such TBP-heterozygous (TBP-Het) cells showed unexpected phenotypic abnormalities, resembling those of cells with delayed mitosis: a significantly lower growth rate, larger size, more G2/-M- than G1-phase cells, and a high proportion of sub-G1, presumably apoptotic, cells. Further evidence for delayed mitosis in TBP-Het cells was provided by the differential effects of several cell cycle-arresting drugs. To determine the cause of these defects, we first examined the status of cdc2 kinase, which regulates the G2/M transition, and unexpectedly observed more hyperphosphorylated, inactive cdc2 in TBP-Het cells. Providing an explanation for this, mRNA and protein levels of cdc25B, the trigger cdc2 phosphatase, were significantly and specifically reduced. These properties were all due to decreased TBP levels, as they could be rescued by expression of exogeneous TBP, including, in most but not all cases, a mutant form lacking the species-specific N-terminal domain. Our results indicate that small changes in TBP concentration can have profound effects on cell growth in vertebrate cells.

Mechanisms of transcriptional activation and repression can both involve TFIID

Regulation of transcription involves the activities of activators and repressors. Recent experiments have provided evidence that the function of both types of regulators can involve interactions with one or more component of the basal transcription machinery. A principal target appears to be TFIID, which consists of the TATA binding protein (TBP) and associated factors (TAFs). Here we describe experiments that provide added support for the idea that interactions affecting TFIID can play important roles in both activation and repression. We show, using transfection assays in Drosophila Schneider cells, that recruitment of TBP to a promoter as a GAL4-TBP fusion protein can provide a substantial activation of transcription. The conserved core of TBP is necessary and sufficient for this effect, which was observed with both TATA-containing and TATA-lacking basal promoters. These findings extend experiments performed in yeast, and strengthen the idea that recruitment of TBP (TFIID) can be an important mechanism of activation. We also provide further support for the idea that TBP can be a target for a transcriptional repressor, the Drosophila Even-skipped protein (Eve). We present evidence that the homeodomain, which is necessary for binding TBP in vitro, can also be required for repression in vivo, independent of its role in DNA binding. On the other hand, deletion of the alanine/proline-rich region that is essential for repression in vivo and TBP binding in vitro does not significantly affect DNA binding by the purified protein. These results strengthen the view that TBP, either directly or indirectly as a component of TFIID, can be a target of both activators and repressors.

The transcriptional repressor even-skipped interacts directly with TATA-binding protein

The Drosophila homeodomain protein Even-skipped (Eve) has previously been shown to function as a sequence-specific transcriptional repressor, and in vitro and in vivo experiments have shown that the protein can actively block basal transcription. However, the mechanism of repression is not known. Here, we present evidence establishing a direct interaction between Eve and the TATA-binding protein (TBP). Using cotransfection assays with minimal basal promoters whose activity can be enhanced by coexpression of TBP, we found that Eve could efficiently block, or squelch, this enhancement. Squelching did not require Eve DNA-binding sites on the reporter plasmids but was dependent on the presence of the Eve repression domain. Further support for an in vivo interaction between the Eve repression domain and TBP was derived from a two-hybrid-type assay with transfected cells. Evidence that Eve and TBP interact directly was provided by in vitro binding assays, which revealed a specific protein-protein interaction that required an intact Eve repression domain and the conserved C terminus of TBP. The Eve homeodomain was also required for these associations, suggesting that it may function in protein-protein interactions. We also show that a previously characterized artificial repression region behaves in a manner similar to that of the Eve repression domain, including its ability to squelch TBP-enhanced expression in vivo and to bind TBP specifically in vitro. Our results suggest a model for transcriptional repression that involves an interaction between Eve and TBP.