Experimental triple-slit interference in a strongly driven V-type artificial atom

Rabi oscillations of a two-level atom appear as a quantum interference effect between the amplitudes associated with atomic superpositions, in analogy with the classic double-slit experiment which manifests a sinusoidal interference pattern. By extension, through direct detection of time-resolved resonance fluorescence from a quantum-dot neutral exciton driven in the Rabi regime, we experimentally demonstrate triple-slit-type quantum interference via quantum erasure in a V-type three-level artificial atom. This result is of fundamental interest in the experimental studies of the properties of V-type three-level systems and may pave the way for further insight into their coherence properties as well as applications for quantum information schemes. It also suggests quantum dots as candidates for multipath-interference experiments for probing foundational concepts in quantum physics.

Figure 1

Illustration of double- and triple-slit interference and generic atomic analogs. (a) Optical double-slit interference experiment where the interference pattern has one sinusoidal component. (b) Double-slit-type interference setup in an atomic system. The time-domain measurement of fluorescence intensity will show show oscillations with one beat note. (c) Optical triple-slit interference experiment where the interference pattern has three sinusoidal components. (d) Simplest configuration of an analog triple-slit-type interference setup in an atomic system. The time-domain measurement of fluorescence intensity will show oscillations with three beat notes. In (b) and (d), the photon emerges from a superposition of excited states with different energies, where $|e_i\rangle$ ($i=1,2,3$) represent the excited states and $|g\rangle$ the ground state. The energy level structure depicted here is for illustrative purposes only and is not an exact representation of the multilevel configuration in our QD.

Figure 2

Double-slit-type excitonic interference: FSS quantum beats. (a) Resonance-fluorescence (RF) detuning spectra in cw mode for $X^0$, and (b) $X^{1-}$ for comparison. The solid black circles and lines are experimental data and Lorentzian fits, respectively. The insets show the corresponding electron and hole spin configurations which have degenerate energies at zero external magnetic field for $X^{1-}$, effectively making it a two-level system. For $X^0$, the electron-hole exchange interaction causes a fine-structure splitting (FSS) of $\sim 13\mu \mathrm{eV}$ at $B=0$ in the QD under study. (c) Quantum erasure scheme. Excitation and detection polarization configuration leading to quantum erasure of which-path information originally encoded in the polarization of photons emerging from $|e_1\rangle ,|e_2\rangle$. (d) Quantum-beat frequency vs external magnetic field. (e)–(h) $X^0$ quantum beats under $\pi$-pulse excitation with 100 ps and $\sim 5\mu \mathrm{eV}$ temporal and spectral widths, observed at various FSS values manipulated by an external magnetic field $B$. The fits to the data are of the form $I\left(t\right)\propto e^{t/T_1}[A+Bcos\left({\delta }_{0}t\right)]$ [30]. Time-resolved measurements were performed with a $\sim 150$-ps-resolution detection setup.

Figure 3

Triple-slit-type excitonic quantum interference: FSS and RS combined quantum beats. Time-resolved resonance fluorescence (TRRF) for (a), (b) driven $X^0$ exciton (V system) showing triple-slit-type interference, combining beats due to both Rabi splitting (RS) and fine-structure splitting (FSS), and (c), (d) the case of a driven $X^{1-}$ (two-level system) showing double-slit-type interference based only on RS quantum beats, shown for comparison. The solid red lines are fits of sinusoidal oscillations to the data having one beat component in (c) and (d) and three beat components with respective frequencies $|\mathrm{\Omega }\pm {\delta }_0/2|$ and $\mathrm{\Omega }$ in (a) and (b). The insets illustrate the effective three- and two-slit energy level configurations, with the dressed states defined as $|\pm \rangle \equiv |g,n+1\rangle \pm |e_{\left(1\right)},n\rangle ,|{\pm }_g\rangle \equiv |g,n\rangle \pm |e_{\left(1\right)},n-1\rangle$, where $n$ is the photon number. (e) and (f) show Rabi frequencies $\mathrm{\Omega }$ extracted from corresponding fits to the data as a function of excitation power for $X^0$ (with FSS $\hslash {\delta }_0=13\mu \mathrm{eV}$) and $X^{1-}$, respectively. The presence of multiple sinusoidal components evidenced by clear deviation from single sinusoidal oscillations in the time-resolved fluorescence for $X^0$ indicates genuine multislit-type interference.

Figure 4

Numerical simulation of TRRF showing RS and FSS quantum beats as well as their combination. Simulation of TRRF using the master-equation method with (a) 100-ps $\pi$ pulse, $X^{1-}$, (b) 100-ps $\pi$ pulse, $X^0$, (c) 2-ns pulse, $X^{1-}$, (d) 2-ns pulse, $X^0$. Here, $\mathrm{\Omega }/\left(2\pi \right)=1.3$ GHz.