Trapping electrons in electrostatic traps over the surface of helium

We have observed trapping of electrons in an electrostatic trap formed over the surface of liquid helium-4. These electrons are detected by a Single Electron Transistor located at the centre of the trap. We can trap any desired number of electrons between 1 and $\sim 30$. By repeatedly ($\sim 10^3-10^4$ times) putting a single electron into the trap and lowering the electrostatic barrier of the trap, we can measure the effective temperature of the electron and the time of its thermalisation after heating up by incoherent radiation.Comment: Presented at QFS06 - Kyoto, to be published in J. Low Temp. Phys., 6 pages, 3 figure

Antibunched photons emitted by a dc-biased Josephson junction

We show experimentally that a dc biased Josephson junction in series with a high-enough-impedance microwave resonator emits antibunched photons. Our resonator is made of a simple microfabricated spiral coil that resonates at 4.4 GHz and reaches a 1.97kΩ characteristic impedance. The second order correlation function of the power leaking out of the resonator drops down to 0.3 at zero delay, which demonstrates the antibunching of the photons emitted by the circuit at a rate of 6×10^7 photons per second. Results are found in quantitative agreement with our theoretical predictions. This simple scheme could offer an efficient and bright single-photon source in the microwave domain

The role of glass dynamics in the anomaly of the dielectric function of solid helium

We propose that acousto-optical coupling of the electric field to strain fields around defects in disordered $^4$He is causing an increase of the dielectric function with decreasing temperature due to the arrested dynamics of defect excitations. A distribution of such low-energy excitations can be described within the framework of a glass susceptibility of a small volume fraction inside solid $^4$He. Upon lowering the temperature the relaxation time $\tau(T)$ of defects diverges and an anomaly occurs in the dielectric function $\epsilon (\omega, T)$ when $\omega \tau(T) \sim 1$. Since $\epsilon (\omega, T)$ satisfies the Kramers-Kronig relation, we predict an accompanying peak in the imaginary part of $\epsilon (\omega, T)$ at the same temperature, where the largest change in the amplitude has been seen at fixed frequency. We also discuss recent measurements of the amplitude of the dynamic dielectric function that indicate a low-temperature anomaly similar to the one seen in the resonance frequency of the torsional oscillator and shear modulus experiments.Comment: 4 pages, 2 figure

Counting Individual Electrons on Liquid Helium

We show that small numbers of electrons, including a single electron, can be held in a novel electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 micron diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor (SET) as an electrometer. A Coulomb staircase is observed as electrons leave the trap one-by-one until the trap is empty. A design for a scalable quantum information processor using arrays of electron traps is presentedComment: 15 pages, 5 figure

Search for supersolidity in 4He in low-frequency sound experiments

We present results of the search for supersolid 4He using low-frequency, low-level mechanical excitation of a solid sample grown and cooled at fixed volume. We have observed low frequency non-linear resonances that constitute anomalous features. These features, which appear below about 0.8 K, are absent in 3He. The frequency, the amplitude at which the nonlinearity sets in, and the upper temperature limit of existence of these resonances depend markedly on the sample history.Comment: Submitted to the Quantum Fluids and Solids Conf. Aug. 2006 Kyot

Transition from phase slips to the Josephson effect in a superfluid 4He weak link

The rich dynamics of flow between two weakly coupled macroscopic quantum reservoirs has led to a range of important technologies. Practical development has so far been limited to superconducting systems, for which the basic building block is the so-called superconducting Josephson weak link. With the recent observation of quantum oscillations in superfluid 4He near 2K, we can now envision analogous practical superfluid helium devices. The characteristic function which determines the dynamics of such systems is the current-phase relation Is(phi), which gives the relationship between the superfluid current Is flowing through a weak link and the quantum phase difference phi across it. Here we report the measurement of the current-phase relation of a superfluid 4He weak link formed by an array of nano-apertures separating two reservoirs of superfluid 4He. As we vary the coupling strength between the two reservoirs, we observe a transition from a strongly coupled regime in which Is(phi) is linear and flow is limited by 2pi phase slips, to a weak coupling regime where Is(phi) becomes the sinusoidal signature of a Josephson weak link.Comment: 12 pages, 4 figure

Generating Two Continuous Entangled Microwave Beams Using a dc-Biased Josephson Junction

We show experimentally that a dc-biased Josephson junction in series with two microwave resonators emits entangled beams of microwaves leaking out of the resonators. In the absence of a stationary phase reference for characterizing the entanglement of the outgoing beams, we measure second-order coherence functions to prove the entanglement. The experimental results are found in quantitative agreement with theory, proving that the low-frequency noise of the dc bias is the main limitation for the coherence time of the entangled beams. This agreement allows us to evaluate the entropy of entanglement of the resonators, estimate the entanglement flux at their output, and to identify the improvements that could bring this device closer to a useful bright source of entangled microwaves for quantum-technological applications

Probing the Microscopic Origin of Gravity via Precision Polarization and Spin Experiments

As in other parts of physics, we advocate the interaction approach: experiments phenomenology low-energy effective (field) theory microscopic theory to probe the microscopic origin of gravity. Using chi-g phenomenological framework, we discuss the tests of equivalence principles. The only experimentally unconstrained degree of freedom is the axion freedom. It has effects on the long-range astrophysical/cosmological propagation of electromagnetic waves and can be tested/measured using future generation of polarization measurement of cosmic background radiation. The verification or refutal of this axionic effect will be a crucial step for constructing effective theory and probing the microscopic origin of gravity. The interaction of spin with gravity is another important clue for probing microscopic origin of gravity. The interplay of experiments, phenomenology and effective theory is expounded. An ideal way to reveal the microscopic origin of gravity is to measure the gyrogravitational ratio of particles. Three potential experimental methods are considered.Comment: 8 pages; 1 figur

Les bases du calcul quantique

URL: http://www-spht.cea.fr/articles/s05/153 Calculation and the quantum computer | Le nanomonde, de la science aux applications. Des nanosciences aux nanotechnologie

Static and dynamic structure factor in solid 4 He: Absence of a glassy phase

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