A step forward for quantum integrated photonics
Integration of quantum devices is a necessary step for future quantum information processing. We report on a glass based device which is able to handle the information encoded in photon polarization. Using this device, we have demonstrated quantum interference with polarization entangled photons.
Photons are the natural candidate for quantum information transmission, quantum computing, optical quantum sensing and metrology. The emerging strategy to overcome the limitations of bulk optical devices residing in critical stability, low precision and physical size consists of taking advantage of the compactness deriving from integrated waveguide technology.
All the experiments performed so far with silica waveguide circuits integrated onto silicon chips are based only on path encoded qubits at a given polarization state of the photons. On the other hand, many quantum information processes and sources of entangled photon states adopt the polarization degree of freedom.
The directional coupler described in this paper, fabricated by femtosecond laser waveguide writing in glass, acts as an integrated beam splitter supporting polarization encoded qubits. The maskless and single step fabrication technique allows to realize circular transverse waveguide profiles able to support the propagation of Gaussian modes in any polarization state.
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LU12935
Routing Entanglement between Multiple Users
Entanglement or ``quantum correlations" between distant locations is a
pivotal resource in quantum information processing useful, for instance,
in networking quantum registers. Spin chains appear to be an ideal toolbox
to model entanglement between distant points; unfortunately, in a generic
spin chain, high quality entanglement between very distant spins is
notoriously much difficult to achieve. In this paper, we exploit the
non-equilibrium dynamics following the sudden switching of a single bond
connecting two Kondo spin chains arranged so that the two impurities are
the boundary spins of the composite system. We show that the dynamics is
able to generate an high quality entanglement between these boundary spins
no matter how distant they are and we use this remarkable feature to
engineer an entanglement router between distant multiple users. Our
analysis shows that it is the Kondo cloud- an extended many-body property
arising from the presence of the impurity- which allows for the observed
high quality distance independent entanglement between the boundary spins
of the composite chain. Our results evidence how a genuinely
non-perturbative phenomenon of condensed matter physics may find relevant
applications in quantum technology.
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AVJ1059
Dissociation of CO2 molecule by near-relativistic electrons
In this paper, we report the first experimental data on total- and partial ionization cross sections of the CO2 molecule under impact of 10-26 keV electrons using an ejected electron-produced ions coincidence technique. The 6-ionic fragments: CO2^+, CO^+, CO2^++, O^+, C^+ and C^++ generated from the dissociative ionization of the CO2 molecule are observed and their relative ionization cross sections are reported as a function of impact energy. This work finds direct relevance to the earth's atmosphere. The CO2 being one of the fundamental constituents of planetary atmospheres, for example of Venus and Mars and of the atmosphere of earth, plays an important role when it interacts with energetic cosmic charged particles, eg., protons, electrons etc. In particular, its level in the earth's atmosphere has been found alarming; its existing level affects the green house adversely and possibly holds the probable cause for creating the current global warming scenario.
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LT12674
How investigating water might have revealed new cancer therapies
Our theoretical work arrives at two distinct but related conclusions:
First, recent experiments which were interpreted as settling an
ongoing controversy over the detailed solvation structure of the
hydroxide ion in water are not as conclusive as originally thought.
These solutions are ubiquitous, including in the human body, because
water pairs can split to form hydroxide and hydronium ions. Second,
the theoretical approach we used to interpret the original
experiments on hydroxide solutions suggests simple diagnostic
criteria for the enhancement of certain energy transfer processes
that occur after solvated molecules are excited with X-rays -- and,
therefore, may allow for the computer-aided design of new combination
radio/chemotherapies for cancer treatment. These conclusions were
obtained by an approximate treatment of the X-ray excited electronic
structure of various chemical species in solution using methods based
on density functional theory; the changes seen in the X-ray excited
electronic structure are key to understanding this energy transfer
mechanism.
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LV11978
Mixing and matching electron waves in artificial atoms
Quantum mechanics teaches us that electrons exhibit wave-like properties. The amplitude of an electron's wave function tells us, where the probability for finding it will be large. Think of the amplitude of a light wave, which determines, where the intensity is high – or, in quantum mechanical terms, where the probability for finding a photon is large.
Another attribute of waves, the phase, is a much subtler property and in many cases gets lost in the measuring process. Photographs, for example, only record the amplitudes and not the phases of the impinging light waves. Only holograms (from greek "holos" = whole + "grafein" writing) manage to preserve both amplitude and phase information.
Our German / Australian team has now shown that when electron wave functions are mapped out, the obtained information can also go beyond determining merely amplitudes, and that the fleeting phase information can have profound influence on the obtained wave function ‘images’. The wave functions we investigated are those of electrons inside so-called quantum dots - small pockets of one semiconductor material, embedded inside another. Just as in atomic physics, electrons trapped in quantum dots organize themselves on different energy levels or "shells". In the so-called p-shell of the dots, the electron can oscillate in two perpendicular modes - similar to a pendulum, which can swing either back and forth or from side to side. When these two linear modes are mixed -or "superimposed"- in just the right way (this is where the phase comes in) the resulting motion becomes circular. The phase also determines whether the motion will be clockwise or counterclockwise. We have shown that the same can be done for the p-shell electrons in quantum dots. An applied magnetic field mixes the linear modes and forces the electrons onto circular orbitals. To map these out, we employed a scheme developed 10 years ago by a group in Nottingham, which uses electrons from a nearby reservoir as a probe. As expected, the images of the wave functions become more and more circular as the magnetic field is increased. But the maps for clockwise and counterclockwise motion look strikingly different. This is unexpected, since the probability of finding an electron should be the same anywhere on the perimeter of its orbit– independent of the sense of rotation. Model calculations were able to resolve this riddle: The electrons from the reservoir, which were used as a reference, are also affected by the applied magnetic field. And only when the phase in the quantum dot matches that of the reservoir, the correct doughnut-shaped probability maps for the circular motion are obtained. When the phase is opposite to that of the reference system, a strongly distorted, more cone-shaped map results. This is similar to holography, where the phase sensitivity is also obtained by comparison with a reference signal.
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BS11311
Inducing phase transitions by bending crystals
Even for brittle ceramic materials, a bending deformation
can stretch the surface of a crystal enough to induce a phase
transition, for example, from an insulating to a metallic state.
This phenomenon can be observed in materials where small changes
in the crystal structure are accompanied by a dramatic change in the
electronic properties. One such material is vanadium dioxide and it
was used in this work to study the effects of repeated stretching
on the dynamics of a metal-to-insulator phase transition.
It is shown that stretching a thin film by bending a single-crystal
oxide substrate is a reliable and simple technique that can be used
to study the electronic response to elastic excitations without the
need for complicated sample preparation or instrumentation.
We expect this technique to be useful for exploring the transport,
dielectric, magnetic, and other properties of various oxide materials
that may find use in new types of sensors and other oxide-electronic
devices.
Figure caption:
A thin film is stretched by bending a single-crystal
substrate. Strain-dependent electrical properties
can be measured by patterning suitable electrodes on the film surface
and attaching flexible leads.
