Tuesday 17th of September 2019

yes, but has the schrödinger's cat with 20 qubits got furballs?...


In 1935, the physicist Erwin Schrödinger put forward the thought experiment with the quantum cat, in which the cat is enclosed in a box together with a radioactive sample, a detector and a lethal amount of poison.


If the radioactive material decays, the detector triggers an alarm and the poison is released. The special feature is that according to the rules of quantum mechanics, unlike everyday experience, it is not clear whether the cat is dead or alive. It would be both at the same time until an experimenter takes a look. A single state would only be obtained starting from the time of this observation.

Since the early 1980s, researchers have been able to realize this superposition of quantum states experimentally in the laboratory using various approaches. "However, these cat states are extremely sensitive. Even the smallest thermal interactions with the environment cause them to collapse," explains Tommaso Calarco from Forschungszentrum Jülich. Among other things, he plays a leading role in Europe's major quantum initiative, the EU's Quantum Flagship programme. "For this reason, it is only possible to realize significantly fewer quantum bits in Schrödinger cat states than those that exist independently of each other". 

Of the latter states, scientists can now control more than 50 in laboratory experiments. However, these quantum bits, or qubits for short, do not display the special characteristics of Schrödinger's cat in contrast to the 20 qubits that the team of researchers have now created using a programmable quantum simulator thus establishing a new record that is still valid even if other physical approaches with optical photons, trapped ions or superconducting quantum circuits are taken into account.


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Image at top by Gus Leonisky: packets of cat food are designed badly. Trying to tell you that the food herein will help your moggie to have less problem with furballs, possibly indicating that the "36 per cent chicken" (don't ask questions about the rest) will prevent your naturally born bird-killer from loosing hair. What about feather-balls, Gus asks? Did Schrödinger think about this?


See also: how good is crap? says scummo...

light brain food...


Optical modulation goes deep in the brain

• Shuo Chen

Neurological disorders will affect more than one-third of us at some point in our lives. In just the next 10 years, the number of patients afflicted with a neurological disorder is projected to reach 1.1 billion worldwide. Yet safe and effective treatments for these conditions are largely lacking.

Deep brain stimulation (DBS) has proved to be one of the most effective therapies to date for neurological disorders ranging from Parkinson's disease to obsessive-compulsive disorder. However, such a treatment requires the implantation of electrodes deep in the brain to electrically stimulate the neurons that are thought to underlie these disorders. In addition to surgical and follow-up costs, which can reach up to $35,000, implantation is highly risky and invasive and the electrical stimulation lacks cell specificity. High-precision, minimally invasive technologies for the modulation of deep brain neurons are needed.


Potential candidates for noninvasive tissue-penetrating stimuli include electric, magnetic, acoustic, and optical signals. Transcranial brain stimulation techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) have been widely used in clinical research but lack spatial resolution and cell specificity, limiting their efficacy.

Optogenetics is a recently developed approach that harnesses genetically encoded light-gated ion channels called rhodopsins to achieve unprecedented precision in stimulating target neurons. The technique has hitherto required the insertion of invasive optical fibers for deep brain applications because the activating blue-green light is strongly scattered and absorbed by endogenous chromophores in brain tissue.

Overcoming the challenge of optical penetration depth will be the key to realizing noninvasive remote optogenetics with high clinical translation potential. Our recent study addressed this problem by applying a nanomaterial-assisted approach that “shifts” the existing optogenetic tools into the near-infrared region.

New Approach to Minimally Invasive DBS

To make optogenetics noninvasive, an obvious option is to use near-infrared light (NIR, 650 to 1350 nm), which can efficiently penetrate biological tissue and reach deep brain regions. However, the development of NIR-responsive rhodopsin variants has proved difficult: The optimal activation wavelengths of recently developed red-shifted rhodopsins all fall short of 650 nm.

We came up with a novel approach in which tissue-penetrating NIR light is locally converted to visible light in the deep brain to activate rhodopsin-expressing neurons (see the figure). To achieve this, we needed an optically unique material that functions much like a light bulb: Low-energy NIR photons turn the bulb on, leading to a high-energy visible emission. Such substances are called “upconversion materials.”

Exploiting “Upconversion” Nanoparticles

Ideal NIR-converting “light bulbs” must be small, efficient in light conversion, highly biocompatible, and have long-term stability. Lanthanide-doped upconversion nanoparticles (UCNPs) met these criteria. UCNPs are capable of converting incident NIR photons into visible emission at an efficiency that is orders of magnitude greater than that of multiphoton processes. As a result, a continuous-wave NIR laser diode of low power can drive intense UCNP-mediated upconversion emission.

To optimize their biocompatibility and long-term stability, we coated UCNPs with silica capable of chemically stabilizing the nanoparticles and preventing direct contact of their lanthanide-doped core with the tissue. The resulting monodispersed blue-emitting UCNPs (NaYF4:Yb/Tm@SiO2) of diameter ∼90 nm showed both minimum cytotoxicity and long-term stability: One month after injection, UCNPs still remained at the target site in the brain.

UCNPS Emit Blue Light Deep in the Brain

We reasoned that UCNP-mediated optogenetics would be feasible for transcranial stimulation of deep brain neurons, based on an evaluation of the upconversion efficiency of UCNPs and the transmittance of NIR light in brain tissue. To test this, we injected blue-emitting UCNPs into the ventral tegmental area (VTA) of the mouse brain, a region located ∼4.2 mm below the skull, and used in vivo fiber photometry to detect visible-light emission. Encouragingly, transcranial delivery of NIR pulses with a peak power of 2.0 W yielded upconverted blue emission of ∼0.063 mW/mm2. This emission strength is sufficient to activate the commonly used channelrhodopsin-2 (ChR2). We were thus motivated to harness UCNPs as optogenetic actuators of transcranial NIR to stimulate deep brain neurons.

Transcranial NIR Modulates Dopamine Release

We chose the VTA for an initial demonstration of transcranial NIR stimulation because of its medical implications. The VTA is a well-established node in the brain's reward system, and the dysregulation of dopamine (DA) release by VTA neurons is causally linked to many neurological disorders, such as major depression.

Science  02 Aug 2019:
Vol. 365, Issue 6452, pp. 456-457

This experiment won the Science and PINS Prize.
See also:from the big bang to strippers: why we need more scientists....