Single photoelectron detection after selective excitation of electron heavy-hole and electron light-hole pairs in double quantum dots

Abstract

The rapid escalation of information processing and storage in the last decade has necessitated the development of novel technologies to ensure highly secured long distance communication. With recent advances in theoretical and experimental studies, quantum information is believed to be a potential candidate for future technology with absolutely secure information exchange. Major challenges in quantum information systems include long distance communication and multi-node networks, which require coherent coupling of photons to solid-state quantum bits (qubits) as used for implementing quantum memory and quantum entanglement. They are both fundamental elements for constructing a quantum repeater, distributed quantum computing and hybrid quantum information network [1].A noticeable proposal for the coherent transfer from photon-polarization qubits to electron spin qubits based on the optical selection rule [2] has been experimentally demonstrated for an ensemble of photons and electrons in g-factor engineered GaAs quantum well (QW) systems [3,4]. However, practical use of a quantum information network requires quantum state transfer from a single photon to a single electron spin, which is feasible in a quantum dot (QD) with three-dimensionally confined electrons [5][6][7]. Electrically gated QDs have an advantage that the confined electron spin can be manipulated and detected for making various kinds of qubit gates. In this context electron spin is an appropriate partner for photons. For the first step toward the verification of coherent transfer between single quanta, A. Pioda et al. [8] realized the real-time detection of trapping and resetting of single photogenerated electrons using a nearby quantum point contact (QPC) as a charge sensor. The change of electron number in the single QD was clearly monitored by measuring the change of the QPC conductance when the photogenerated electron escaped from the dot. The authors proved that the photoelectron trapping can be electrically detected within a time significantly shorter than the spin-flip time T 1 . This technique was later extended to double QDs (DQDs) and the improved ability to detect single photoelectrons as well as their spin orientations through inter-dot tunneling has been demonstrated [9]. Note in DQDs spin-related phenomena such as Pauli spin blockade, and electron spin resonance can be utilized for nondestructive spin readout, and coherent spin rotation, respectively [10][11][12][13].Despite the previous innovative results, those samples are not suitable for coherent transfer. The proposed coherent transfer scheme postulates specified systems like QWs with a GaAs well between two AlGaAs barriers. The heavy and light hole bands are energetically separated in the QW and the electron and light hole g-factors can be tuned to satisfy the condition of coherent photon to spin information transfer: 2,4]. Here, g e , and g lh are the g-factors of conduction band electron, and valence band light hole, respectively,  B the Bohr magneton, and E ph the photon ene...

Single electron-photon pair creation from a single polarization-entangled photon pair

“…3(a) is consistent with the PL spectrum (see SI). Besides, we previously experimentally verified HH and LH resonant excitation on GaAs lateral QDs 26 , and the resonance peak in Fig. 3(a) is similar to the reported result.…”

“…The mechanism of photo-electron trapping in this experiment is explained in detail in ref. 26 . Photo-electrons are created in the dot by optical excitation of electron-hole pairs in the GaAs QW at the Γ-point.…”

“…One of the paired photons is irradiated on the GaAs QD, while the other on a single photon counter. Real-time measurements of the photo-electron in the dot by a charge sensor 21 – 26 and the photon by the photon counter are performed simultaneously to identify the temporal coincidence between the photo-electron detection and the photon detection. Although a fast real-time detection technique of an electron has been established for gate defined QDs in recent years, photo-electron detection is still technically difficult because QDs made in a doped quantum well becomes eventually unstable due to charge noise and persistent photo-conductivity when shining light pulses.…”

Angular momentum transfer from photon polarization to an electron spin in a gate-defined quantum dot

“…We set the photon energy to this peak in the experiment of spin readout of a single photo-electron. The LH exciton is expected to be at around 1.602 eV from simulation and additional measurements 18 , but not well resolved.…”

“…Single electrons are optically accessible in gate-defined QDs because the electronic potential acts as a trapping potential for the electrons, while it is repulsive for the holes upon single electron–hole pair excitation in the QD area 15,16 . Then single photo-electrons can be generated from the individual heavy-hole (HH) and light-hole (LH) excitons 17,18 , and detected using a nearby charge sensor because the photo-electron trapping results in a charge addition for the dot. The photo-electron spin orientation can be judged using the spin-dependent tunneling from the dot to the lead whose Fermi energy is aligned between the Zeeman sub-levels in the dot 19 .…”