Condensed Matter Physics Seminar

Stefan Ludwig, LMU Munchen

Thursday 25 April 2013, 1500-1600
Cavendish Colloquium Room

Title: Single phonon quantum interference and back-action in quantum-dot electrical circuits


Lateral few-electron quantum-dot circuits are promising candidates for metrology and quantum information applications. Qubit readout typically involves a charge measurement made probing the current through a nearby biased quantum point contact (QPC). For quantum applications it is critical to understand the back-action disturbances resulting from such a measurement approach. It is well-established that QPC detectors emit phonons which are possibly reabsorbed by nearby qubits [1]. Here, we present the observation of a pronounced back-action effect in multiple dot circuits, where the absorption of detector-generated phonons is strongly modified by a quantum interference effect [2]. The reported phenomenon is well described by a theory incorporating both the QPC and coherent phonon absorption in coupled dots. It also promises applications: destructive interference allows strategies to suppress back-action during the qubit readout procedure. Furthermore, our experiments reveal the usability of coupled dots as a single phonon detector and spectrometer.

[1] D. Harbusch, et al., PRL textbf{104}, 196801 (2010);

[2] G. Granger, et al., Nat. Phys. textbf{8}, 522 (2012).