GEOMDISS Results

First year achievements

Second year achievements

Third year achievements


  1. First clear experimental observation of non-commuting quantum gates based on non-Abelian non-adiabatic geometric phase gates (see figure 1 and 2 below).
  2. Characterization of the effect of noise on the Berry phase along different directions and for different paths using a superconducting qubit. Comparison with a dynamical phase gate evidences the robustness of the geometric quantum gates.
  3. Pumping on the level of a single Cooper pair per cycle achieved experimentally. Quantized pumping demonstrated (see figure 3).
  4. Breakdown of adiabatic pumping due to Landau-Zener processes as well as due to quasiparticle generation experimentally investigated.
  5. Influence of dissipation on pumping in both adiabatic and non-adiabatic limits theoretically understood.
  6. Topologically quantized pumping in various topological systems, e.g., with Majorana bound states, proposed and theoretically investigated.
  7. Resonant spin pumping investigated by means of a functional renormalization group (FRG).
  8. APRES spectra of 3D topological insulator experimentally obtained and analyzed. Surface states and surface spin structure demonstrated.

 

cavity_transmon.png

Fig 1: (a) Aluminium cavity with an embedded sapphire chip containing two transmon qubits. The left qubit is not used in the experiment. The electric field profile, E, of the fundamental mode is sketched (red) in the upper part of the cavity.
(b) Optical micrograph of the transmon device.
(c) Scanning electron micrograph of the Josephson junction.

Elements_Gates.png

  
Fig 2:(a) Diagonal elements χii of the process matrices for ideal (lines) and experimental (symbols) geometric gates as a function of Θ with Φ= π.
(b,c) Bar chart of the real part of the reduced measured process matrices of the geometric Hadamard gate H (b) and the NOT gate (c) with fidelities of 95% and 98%, respectively. The wire frames show the theoretically expected values.


Fig 3: Pumped charge versus gate amplitude Δ ng and gate offset ng0. The shapes of diamonds correspond to a quantized pumped charge in units of Cooper pairs. Remarkably, the plot is 2e-periodic not only in the gate amplitude, but also in the gate offset, a clear signature of the absence of quasi-particle poisoning. The accuracy of the quantization is currently of the order of a few percent, thus quite far from metrological standard.

   diamond_charge.png