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Format: 2019-11-12
Format: 2019-11-12
Format: 2019-11-12


16th May 2011

Article on research done by the group of prof. Jens Eisert, one of the scientists involved in Q-ESSENCE, highlighted at physicsworld.com.


10th May 2011

QUIE2T was represented with an exhibit at the Commission’s fet11 conference taking place from 4 to 6 of May in Budapest. As part of the activities the attached project flyer that served as a press release was distributed at the conference.


10th May 2011

QUIE2T was represented at the Commission’s fet11 conference taking place from 4 to 6 of May in Budapest. An exhibit proposal that was submitted in response to a European Commissions call has been successfully evaluated and was among the 28 exhibition stands present at the conference. According to the commission, “fet11 is a unique conference on visionary, high-risk and long-term research in information science and technology.


3rd May 2011

We review quantum information processing with cold neutral particles, that is, atoms or polar molecules. First, we analyze the best suited degrees of freedom of these particles for storing quantum information, and then we discuss both single- and two-qubit gate implementations. We focus our discussion mainly on collisional quantum gates, which are best suited for atom-chip-like devices, as well as on gate proposals conceived for optical lattices.


21st Apr 2011

Atom chips are a promising candidate for a scalable architecture for quantum information processing provided a universal set of gates can be implemented with high fidelity. The difficult part in achieving universality is the entangling two-qubit gate. We consider a Rydberg phase gate for two atoms trapped on a chip and employ optimal control theory to find the shortest gate that still yields a reasonable gate error. Our parameters correspond to a situation where the Rydberg blockade regime is not yet reached.


21st Apr 2011

Optimal control theory is a versatile tool that presents a route to significantly improving figures of merit for quantum information tasks. We combine it here with the geometric theory for local equivalence classes of two-qubit operations to derive an optimization algorithm that determines the best entangling two-qubit gate for a given physical setting. We demonstrate the power of this approach for trapped polar molecules and neutral atoms.


6th Apr 2011

Enclosed you will find a list of Q-ESSENCE publications from the first year of project duration.


1st Apr 2011

We report a 2 GHz operation of InGaAs avalanche photodiodes for efficient single photon detection at telecom wavelengths. Employing a self-differencing circuit that incorporates tuneability in both frequency and arm balancing, extremely weak avalanches can now be sensed so as to suppress afterpulsing. The afterpulse probability is characterized as 4.84% and 1.42% for a photon detection efficiency of 23.5% and 11.8%, respectively. The device will further increase the secure bit rate for fiber wavelength quantum key distribution.


1st Apr 2011

[Correspondence]


1st Apr 2011

We show that semiconductor avalanche photodiodes can exhibit diminutive amplification noise during the early evolution of avalanches. The noise is so low that the number of locally excited charges that seed each avalanche can be resolved. These findings constitute an important step towards realization of a solid-state noiseless amplifier for quantum information processing. Moreover, we believe that the experimental setup used, i.e., time-resolving locally excited avalanches, will become a useful tool for optimizing the number resolution.


1st Apr 2011

We study controlled phasegates for ultracold atoms in an optical potential. A shaped laser pulse drives transitions between the ground and electronically excited states where the atoms are subject to a long-range 1/R3 interaction. We fully account for this interaction and use optimal control theory to calculate the pulse shapes. This allows us to determine the minimum pulse duration, respectively, gate time T that is required to obtain high fidelity.


30th Mar 2011

We demonstrate a 1550 nm correlated photon-pair source in an integrated glass platform—a chalcogenide As2S3 waveguide. A measured pair coincidence rate of 80 s−1 was achieved using 57 mW of continuous-wave pump. The coincidence to accidental ratio was shown to be limited by spontaneous Raman scattering effects that are expected to be mitigated by using a pulsed pump source.


30th Mar 2011

Photon sources for multi-photon entanglement experiments are commonly based on the process of spontaneous parametric down conversion. Due to the probabilistic photon production, such experiments suffer from low multiphoton count rates. To increase this count rate, we present a novel SPDC pump source based on a femtosecond UV enhancement cavity that increases the available pump power while maintaining a high repetition rate of 80MHz. We apply the cavity as photon source for realizing symmetric, multi-partite entangled Dicke states, which are observed with a high rate and high fidelity.


30th Mar 2011

We examine whether metrological resolution beyond coherent states is a nonclassical effect. We show that this is true for linear detection schemes but false for nonlinear schemes, and propose a very simple experimental setup to test it. We find a nonclassicality criterion derived from quantum Fisher information.


30th Mar 2011

We present schemes for efficient state teleportation and entanglement swapping using a single quantum-dot spin in an optical microcavity based on giant circular birefringence. State teleportation or entanglement swapping is heralded by the sequential detection of two photons and is finished after the spin measurement. The spin-cavity unit works as a complete Bell-state analyzer with a built-in spin memory allowing loss-resistant repeater operation.

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