### 0.0909090909: Shroedinger's cat

Following Uri Geller (via Peter Woit), today it could be open a portal to another universe!
Geller support his original idea with a mix of string theory and numerology. At the other hand, this mixture of science and superstition is perfect for a fiction, for example The Invisibles, the cult comics written by Grant Morrison in the past century. The comic book series, behind the entertainment pourposes, hides a political purpose, to tell the world and the use of mass media in order to control people. But I don't write about this subject, but about the scientific background, in particular I would start from the many worlds hypothesis(1).
In The Invisibles there is, indeed, a war against alien from another universe. The scientific basis of the comics is the string theory: for example the simbols of early cristians is interpreted like a part of the infinity symbol, that it also represents the connection between the two universes, like two universal strings or two membranes (or branes). But the story of the scientific multiversity began woth the famous Schroedinger's cat: The thought experiment was proposed by Schroedinger in 1935 in order to proof the limits of quantum mechanics and Copenaghen interpretation, but Erwind could not know that his paradox would be generate a lot of intriguing theoretical science. One consequence is the many worlds interpretation, but another research line is the construction of a real Schroedinger's cat!
A first right attempt was made by Jonathan Friedman and collegues(2) (read physicsworld). The team realized a superconducting quantum interference device (SQUID):
The simplest SQUID is a superconducting loop of inductance $L$ broken by a Josephson tunnel junction with capacitance $C$ and critical current $I_c$. In equilibrium, a dissipationless supercurrent can flow around this loop, driven by the difference between the flux that threads the loops and the external flux $\phi_x$ applied to the loop.
They used two junctions in their experimental setup, and so they realized a superposition between two different states:
Such a superposition would manifest itself in an anticrossing, where the energy-level diagram of two levels of different fluxoid states (labelled $| 0 >$ and $| 1 >$) is shown in the neighbourhood in which they would become degenerate without coherent interaction (dashed lines). Coherent tunnelling lifts the degeneracy (solid lines) so that at the degeneracy point the energy eigenstates are $\frac{1}{2} \left ( | 0 > + | 1 > \right )$ and $\frac{1}{2} \left ( | 0 > - | 1 > \right ) \, ,$ the symmetric and anti-symmetric superpositions. The energy difference $E$ between the two states is given approximately by $E = \epsilon^2 + \Delta^2$, where $\Delta$ is known as the tunnel splitting.
In order to proof the existence of the splitting, a necessary condition is that:
(...) the experimental linewidth of the states be smaller than $\Delta$(3). The SQUID is extremely sensitive to external noise and dissipation (including that due to the measurement of ), both of which broaden the linewidth. Thus, the experimental challenges to observing coherent tunnelling are severe. The measurement apparatus must be weakly coupled to the system to preserve coherence, while the signal strength must be sufficiently large to resolve the closely spaced levels. In addition, the system must be well shielded from external noise. These challenges have frustrated previous attempts5, 6 to observe coherence in SQUIDs.
But the observation presents some difficulties, like the SQUID's sensibility to the noise, which must be shielded, and to the dissipation; the device must also preserve the coherence,
(...) while the signal strength must be sufficiently large to resolve the closely spaced levels.
All of these problems influenced previous attempts(4, 5), but they found an answer thanks Friedman's team:
In the plot it is showed the probability to realize a transition like function of the flux $\phi_x$. The curves, plotted for different potentials, are shifted upwards in order to clarify the shapes. The quantum behaviour of the macroscopic system is argued by the existence of two peaks, that decreasing potential separate one from each other and reach the same amplitude. The two peaks correspond to two distinct macroscopic fluxes and we can conclude that they realize a macroscopic Schroedinger's cat.
A most recent attempt has made this year (via tumblr) by a team of China's researchers leaded by Xing-Can Yao(6). The team, using the following experimental setup:
realized a eight photons' entanglement. Passing through a series of non-linear cristals, the photons entanlged, but with low energy. So the researchers decided to design a ultraviolet laser source that could produce an higher number of couples of entangled photons than usual lasers.
In conclusion, by exploiting the new techniques of ultra-bright entangled photon source, noise-reduction multi-photon interferometer and post-selection detection, we have experimentally generated and characterized the eight-photon Schrodinger-cat state. (...) One immediate application is to demonstrate the topological error correction scheme(9) with eight-photon graph states. Furthermore, our eight-photon setup can serve a well-controlled few-qubit quantum simulation testbed for studying interesting phenomena in solid-state physics(8), quantum chemistry(7), and even biophysics(11). Finally, it should also allow tests of the stability and dynamics of diff erent families of entangled states (such as Schrodinger-cat states and one- and two-dimensional cluster states) under the eff ect of decoherence(10), which may provide new insights into our understanding of the intriguing questions of classical to quantum transition.
In conclusion I propose you Schroedinger's cat by Tears for Sears:
See more:
Schroedinger's cat di John H. Lienhard (è possibile scaricare anche la versione audio)
(1) This interpretation is origined by Hugh Everett's research work (thesis and a paper on Review of Modern Physics - pdf)
(2) Friedman, J., Patel, V., Chen, W., Tolpygo, S., & Lukens, J. (2000). Quantum superposition of distinct macroscopic states Nature, 406 (6791), 43-46 DOI: 10.1038/35017505
(3) Averin, D. , Friedman, J. R. & Lukens, J. E. Macroscopic resonant tunneling of magnetic flux (2000)
(4) Rouse, R. , Han, S. & Lukens, J. E. Observation of resonant tunneling between macroscopically distinct quantum levels. Phys. Rev. Lett. 75, 1614–1617 (1995).
(5) Rouse, R. , Han, S. & Lukens, J. E. in Phenomenology of Unification from Present to Future (eds Palazzi, G. D., Cosmelli, C. & Zanello, L.) 207– 224 (World Scientific, Singapore, 1998).
(6) Xing-Can Yao, Tian-Xiong Wang, Ping Xu, He Lu, Ge-Sheng Pan, Xiao-Hui Bao, Cheng-Zhi Peng, Chao-Yang Lu, Yu-Ao Chen, Jian-Wei Pan, Observation of eight-photon entanglement (7) B. P. Lanyon et al., Nature Chemistry 2, 106 (2010).
(8) X.-S. Ma et al., Nature Physics 7, 399 (2011).
(9) R. Raussendorf, J. Harrington and K. Goyal, New J. Phys. 9, 199 (2007).
(10) J. T. Barreiro et al., Nature Physics 6, 943 (2010).
(11) J. Cai, G. G. Guerreschi and H. J. Briegel, Phys. Rev. Lett. 104, 220502 (2010).