Category Archives: quantum measurement

Canadian researchers devise method to directly measure the quantum wavefunction

From PhysOrg.com:

To get around that problem, the team, led by Jeff Lundeen, devised a method based on “weak” measurements, whereby an observation is made that only alters the particle just a little tiny bit and gives information about just one property of the particle at a time. Taking multiple such measurements of identical copies of a particle, such as a photon, gives more and more information, eventually approaching a very close approximation to the actual state of the system. In one respect this approach is similar to the way calculus is used to measure irregularly shaped objects by cutting it into a number that approaches infinity, virtual slices, then adding up the results. When combined with more certain “strong” measurement results, the procedure provides an accurate measurement of the wavefunction.

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Exotic behavior when mechanical devices reach the nanoscale

From PhysOrg.com:

Most mechanical resonators damp (slow down) in a well-understood linear manner, but ground-breaking work by Prof. Adrian Bachtold and his research group at the Catalan Institute of Nanotechnology has shown that resonators formed from nanoscale graphene and carbon nanotubes exhibit nonlinear damping, opening up exciting possibilities for super-sensitive detectors of force or mass.

The finding has profound consequences. Damping is central to the physics of nanoelectromechanical resonators, lying at the core of quantum and sensing experiments. Therefore many predictions that have been made for nanoscale electro-mechanical devices now need to be revisited when considering nanotube and graphene resonators.

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Single atom stores quantum information

From PhysOrg.com:

A data memory can hardly be any smaller: researchers working with Gerhard Rempe at the Max Planck Institute of Quantum Optics in Garching have stored quantum information in a single atom. The researchers wrote the quantum state of single photons, i.e. particles of light, into a rubidium atom and read it out again after a certain storage time. This technique can be used in principle to design powerful quantum computers and to network them with each other across large distances.

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Proposed gamma-ray laser could emit ‘nuclear light’

From PhysOrg.com:

Building a nuclear gamma-ray laser has been a challenge for scientists for a long time, but a new proposal for such a device has overcome some of the most difficult problems. In the new study, Eugene Tkalya from the Institute of Nuclear Physics at Moscow State University has theoretically proven how the stimulated gamma emission of thorium nuclei can emit coherent visible light. Although the nuclear gamma-ray laser emits light based on stimulated emission, it operates a bit differently than a normal laser.

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Scientists view a quantum jump in real time

From PhysOrg.com:

Hopefully, this will lead us one step closer to realizing a quantum computer. “In order to correct errors which will occur in any realistic quantum computer, we need to detect them quickly and efficiently,” Siddiqi points out. “Now that we have shown that it is possible to track changes in the quantum state in real time, it should be possible to apply this functionality to quantum information processing.”

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Fattening up Schrödinger’s cat

From Nature News:

Researchers in Austria have made what they call the “fattest Schrödinger cats realized to date”. They have demonstrated quantum superposition – in which an object exists in two or more states simultaneously – for molecules composed of up to 430 atoms each, several times larger than molecules used in previous such experiments1.

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New fundamental limitation restricts position accuracy of quantum objects

From PhysOrg.com:

Although the uncertainty principle is probably the most well-known example of a fundamental limitation of measurement precision in quantum mechanics, it is not the only one. In fact, every physical system is characterized by a number of variables that do not change their values as the system evolves over time; such variables are called conserved quantities and they are said to obey a conservation law. The fact that some quantities cannot change their values suggests that there might be restrictions on the possible ways in which a measurement device can interact with a quantum object and extract information from it.

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