Figure 1

Scanning electron microscope micrograph of the actual MZI and the detector. The inner contact ($D1$) and the two QPCs are connected with air bridges. The sample is defined by etching the GaAs-AlGaAs heterostructure that embeds a high mobility 2D electron gas. Magnetic field of $\sim 3\mathrm{T}$ leads to filling factor 2 in the bulk (electron temperature $\sim 15\mathrm{mK}$). The signal at $D2$ is filtered by a cold LC resonant circuit at a center frequency $\sim 1\mathrm{MHz}$ and bandwidth $\sim 100\mathrm{kHz}$. It is amplified in situ by a low noise preamplifier cooled to 4.2 K.Reuse & Permissions

Figure 2

Path determination leading to dephasing. (a) The transmission of the interferometer $T_{\mathrm{MZI}}$ oscillates as function of the modulation gate voltage with visibility $\nu \sim 35\%$ at $V_{S2}=4.5\mu \mathrm{V}$ (at $V_{S2}=0$, $\nu \sim 45\%$, not shown). The Fourier transform has a peak at $\sim 0.8$ oscillation per 1 mV (inset). (b) At $V_{\det }=24\mu \mathrm{V}$ the oscillations drop by more then an order of magnitude. The phase shift between Figs. 2a, 2b is meaningless, as the two graphs where measured at different times; hence slightly different magnetic fields. (c) The evolution of the visibility as function of $V_{\det }$ (the small increase in the visibility near $V_{\det }=5\mu \mathrm{V}$ is due to resonances in point contact QPC0 at small $V_{\det }$). Upper inset: The dependence of the visibility on $T_{\mathrm{QPC}0}$ for $V_{\det }=6\mu \mathrm{V}$ (gray dots) and for $15\mu \mathrm{V}$ (black dots). The dotted line is the prediction of Eq. (4) with $\gamma =\pi$ and $n=1$. Lower inset: Measured noise of the detector agrees with shot noise of independent electrons at $T=15\mathrm{mK}$.Reuse & Permissions

Figure 3

Oscillatory component of the total noise. The total noise measured at $D2$ (at $\sim 1\mathrm{MHz}$, $\sim 30\mathrm{kHz}$ bandwidth) as a function of $V_{S3}$ with $V_{S2}=4.5\mu \mathrm{V}$. It contains the contributions of the MZI, the detector, and their cross correlation. (a) For $V_{\det }\sim 2\mu \mathrm{V}$, there is no dephasing. The noise is mostly that of the MZI (plotted around the average), having only a second $AB$ harmonic. (b) For $V_{\det }=24\mu \mathrm{V}$, the $AB$ oscillations of the conductance nearly vanish [Fig. 2b], however, the shot noise oscillates at the basic $AB$ periodicity (plotted around the average).Reuse & Permissions

Figure 4

Evolution of the $AB$ harmonics in the total noise as a function of the detector voltage $V_{\det }$. (a) The strength of the first $AB$ harmonic. (b) The strength of the second $AB$ harmonic. The following rapid increase at $V_{\det }\sim 18\mu \mathrm{V}$ and the subsequent decrease are still not understood (see text).Reuse & Permissions