Interference Effects in a Tunable Quantum Point Contact Integrated with an Electronic Cavity

Chengyu Yan, Sanjeev Kumar, Michael Pepper, Patrick See, Ian Farrer, David Ritchie, Jonathan Griffiths, and Geraint Jones

Phys. Rev. Applied 8, 024009 – Published 17 August 2017

Abstract

We show experimentally how quantum interference can be produced using an integrated quantum system comprising an arch-shaped short quantum wire (or quantum point contact, QPC) of 1D electrons and a reflector forming an electronic cavity. On tuning the coupling between the QPC and the electronic cavity, fine oscillations are observed when the arch QPC is operated in the quasi-1D regime. These oscillations correspond to interference between the 1D states and a state which is similar to the Fabry-Perot state and suppressed by a small transverse magnetic field of $\pm 60 mT$ . Tuning the reflector, we find a peak in resistance which follows the behavior expected for a Fano resonance. We suggest that this is an interesting example of a Fano resonance in an open system which corresponds to interference at or near the Ohmic contacts due to a directly propagating, reflected discrete path and the continuum states of the cavity corresponding to multiple scattering. Remarkably, the Fano factor shows an oscillatory behavior taking peaks for each fine oscillation, thus, confirming coupling between the discrete and continuum states. The results indicate that such a simple quantum device can be used as building blocks to create more complex integrated quantum circuits for possible applications ranging from quantum-information processing to realizing the fundamentals of complex quantum systems.

Received 12 April 2017

DOI:https://doi.org/10.1103/PhysRevApplied.8.024009

Physics Subject Headings (PhySH)

Ballistic transport Hybrid quantum systems Quantum information processing Quantum interference effects

Quantum wires Two-dimensional electron gas

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Chengyu Yan^1,2,*, Sanjeev Kumar^1,2, Michael Pepper^1,2, Patrick See³, Ian Farrer^4,†, David Ritchie⁴, Jonathan Griffiths⁴, and Geraint Jones⁴

¹London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom
²Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, United Kingdom
³National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
⁴Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 OHE, United Kingdom

^*uceeya3@ucl.ac.uk
^†Present address: Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, United Kingdom.

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 8, Iss. 2 — August 2017

Subject Areas

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Schematic of device and experiment setup. (a) The yellow square blocks at the edge of mesa marked 1–6 are Ohmic contacts, whereas the golden metallic patterns within the mesa form a pair of arch-shaped gates and a reflector. The red dotted lines show the possible boundary of cavity formed between the QPC and the reflector. Excitation current is fed to Ohmic 1, while 2 is grounded; Ohmics 3 and 4 are voltage probes. (b) Differential conductance measurement of the QPC (main plot) and reflector (inset). The series resistance is not removed. It should be noticed that the standard two-terminal measurement is performed with Ohmics 1 and 5 [30]. The red dashed line in the inset corresponds to $V_{r} = - 0.27 V$ .
Reuse & Permissions
Figure 2
$R$ as a function of arch QPC voltage for various $V_{r}$ . (a) When $- 0.29 V \leq V_{r} \leq - 0.27 V$ , a pronounced double-peak structure and fine oscillations are observed. (b) When $V_{r} > - 0.27 V$ , all the features gradually smear out. Data are offset vertically by $20 Ω$ for clarity.
Reuse & Permissions
Figure 3
$R$ as a function of $V_{r}$ . (a) The arch-gate voltage is fixed at $- 0.65$ , $- 0.43$ , $- 0.36$ , $- 0.24$ , $- 0.21$ , and 0 V while sweeping $V_{r}$ . Data are offset vertically for clarity. The right axis displays the reflector conductance as a function of $V_{r}$ as indicated by a red arrow. (b) Upper plots show the theoretical fitting (solid line) of $Δ R (V_{r}, V_{a}) = R (V_{r}, V_{a}) - R (V_{r}, 0)$ , where $V_{a} = - 0.65$ and $- 0.50 V$ , respectively; $Δ R$ follows a well-defined Fano line shape. The lower plot shows Fano factor $q$ as a function of $V_{a}$ .
Reuse & Permissions
Figure 4
Effect of perpendicular magnetic field. The reflector voltage is set to $- 0.28 V$ , and the field is increased from 0 mT (bottom trace) to $- 200 mT$ (top trace) by steps of $- 20 mT$ . It is clear that the fine oscillations disappear around $- 60 mT$ (marked by an arrow). Peak I of the double-peak structure weakens with increasing field, while peak II gets enhanced by magnetic field and shifts towards less negative $V_{a}$ as indicated by a dashed black curve.
Reuse & Permissions
Figure 5
Magnetoresistance of the arch QPC reflector assembly. (a) The reflector is grounded or set to $- 0.25 V$ ; the results show a typical Hall voltage development as the magnetic field is swept for different QPC voltage. Data for $V_{r} = - 0.25 V$ are offset vertically by $50 Ω$ for clarity. (b) The reflector is set to $- 0.3 V$ , QPC voltage $V_{a}$ is set at $- 0.63 V$ (at fine oscillations), $- 0.24 V$ (peak I), $- 0.21 V$ (peak II), and 0 V, respectively. Data are offset vertically by $100 Ω$ for clarity. (c) Theoretical fitting of $Δ R (V_{a}, B) = R (V_{a}, B) - R (0, B)$ , where $V_{a} = - 0.24 V$ , showing the experimental data follow a Fano line shape, the Fano factor $q = 0.823$ .
Reuse & Permissions
Figure 6
Temperature dependence of $R$ . (a) The evolution of nonlocal resistance at $V_{r} = - 0.3 V$ against temperature; the lattice temperature increases from 20 mK (top trace) to 1.8 K (bottom trace). Data are offset vertically for clarity. (b) Theoretical fitting of the height of peak I of the double-peak structure using Eqs. (3) and (4) with $p = 1$ for the fitting.
Reuse & Permissions

Physical Review Applied