Tunneling with the Help of Photons

Bao‐Chuan Wang, Gang Cao, Bao-Bao Chen +4 more

The gate-defined quantum dot is regarded as one of the basic structures required for scalable semiconductor quantum processors. Here, we demonstrate a structure that contains three quantum dots scaled in series. The electron number of each dot and the tunnel coupling between them can be tuned conveniently using splitting gates. We tune the quantum dot array asymmetrically such that the tunnel coupling between the right dot and the central dot is much larger than that between the left dot and the central dot. When driven by microwaves, the sidebands of the photon-assisted tunneling process appear not only in the left-to-central dot transition region but also in the left-to-right dot transition region. These sidebands are both attributed to the left-to-central transition for asymmetric coupling. Our result shows that there is a region of a triple quantum dot structure that remains indistinct when studied with a normal two-dimensional charge stability diagram; this will be helpful in future studies of the scalability of quantum dot systems.

Benjamin Bähr, Boris Lemmer, Rina Piccolo

Z.Y. Wang

de Broglie formula to photons in an unbounded space is E=hν and λ=h/p. According to electrodynamics, nevertheless,we prove the ratio E/p in a waveguide is greater than the product νλ which implies E=hν and p=h/λ cannot be tenable at the same time. Then the Casimir effect is applied to confirm E=hν and p<h/λ. It is helpful to study quantum tunnelling and superluminality[1]~[2], Cavity-QED, origin of mass, etc. The microwave experiment to test is also presented.

Malin Premaratne, Govind Prasad Agrawal

K. Segall, J. Moyer, J. J. Mazo

Superconducting tunnel junctions (STJs) have been successfully used as single-photon detectors but require the use of a magnetic field to operate. A recent paper has proposed the idea to use a circuit of three junctions in place of a single junction in order to achieve the necessary biasing without applying a magnetic field. The nonlinear interaction between the different junctions in the circuit causes the existence of a stable subgap state for one of the junctions, which acts as the detector junction. In this paper, we present the first measurements demonstrating the existence of such a biasing state feasible for STJ detectors. Single junction measurements with an applied magnetic field help determine the functional form of the subgap current versus voltage; then the operating point of a three-junction circuit is measured and fit to theory. The excellent match between theory and experiment demonstrates the existence of the subgap biasing state. The outlook for possible use in detector applications is discussed.