Quantum key distribution (QKD) enables the transmission of information that is secure against general attacks by eavesdroppers. The use of on-demand quantum light sources in QKD protocols is expected to help improve security and maximum tolerable loss. Semiconductor quantum dots (QDs) are a promising building block for quantum communication applications because of the deterministic emission of...
Quantum information distribution over quantum networks is essential for the advancement of secure communication and distributed quantum computing. To achieve this, reliable and efficient sources of flying qubits are crucial. GaAs quantum dots are promising candidates due to their outstanding features [1, 2, 3]. However, these quantum dots often exhibit dissimilar emission properties, so that...
Epitaxially grown semiconductor quantum dots (QDs) have demonstrated to be excellent sources of single photons and entangled photon pairs for quantum information and computational applications. With demonstrated on-demand single photon purities [1] and indistinguishabilities [2] exceeding 99%, QDs are a natural inclusion in quantum integrated photonics, allowing for future device scalability....
As quantum technology gains more importance, single photon sources such as semiconductor quantum dots become more relevant. One of the advantages of using single photons as qubit is the ability of photons to bridge long distances, hence the reason they are also referred to as flying qubits. Bridging long distances can be achieved by utilizing silica fibers, a mature technology which...
Applications in quantum computing and communication require entangled photon pairs featuring simultaneously a high degree of entanglement as well as a high single photon indistinguishability. Epitaxially grown quantum dots (QDs), especially gated GaAs QDs have shown to both be able to emit highly indistinguishable single photons as well as highly polarization entangled photon pairs from the...
Site-controlled Pyramidal QDs are a class of solid state quantum emitters that are photo-lithographically defined on (111)B GaAs, grown through MOVPE inside selectively etched tetrahedral recesses. This system has the unique ability to finely control the nominal thickness of the dots, the barriers and their composition. However, pre-processed QDs rarely satisfy the requirements that are vital...
Towards quantum information processing in silicon-on-insulator (SOI), single photons play an important role as carriers of information. Thereby, a key element is an integrated, efficient single-photon source (SPS) with high purity and fidelity operating on demand. Although sources of entangled photon pairs and heralded single photons have been successfully developed and integrated on SOI...
Advances in silicon photonics have so far largely focused on the development of classical optoelectronic devices. While there has been great success in this classical field of photonics, the development of silicon-compatible quantum photonics components, which can be combined with cost-efficient silicon electronics, has faced significant challenges, particularly regarding the growth of...
Quantum cryptography and optical quantum computing require well-performing single and entangled photon sources, placing stringent demands on semiconductor quantum dots (QDs) embedded in microcavities such as circular Bragg grating (CBG) resonators [1,2]. Their low optical mode volume facilitates enhanced coupling between quantum dot and resonator. At the same time, it necessitates accurate...
We report on an experiment in which orbital-angular-momentum (OAM)-entangled photon pairs generated by the spontaneous parametric down-conversion process can be engineered to have particular symmetry properties. Our method is based on the use of a Dove-prism pair in conjunction with Hong-Ou-Mandel (HOM) interferometry resolved in transverse position and OAM. The latter allows us to engineer...
Integrated quantum photonic circuits (IQPCs) are very promising candidates for scalable and flexible on-chip quantum computation and quantum communication hardware. One critical requirement for their realization is the scalable integration of quantum emitters delivering single indistinguishable photons on-demand. This is potentially possible through the resonant excitation of an integrated...
The interaction between the charge carrier spin of a quantum dot (QD) exciton and photons enables the transfer of quantum information between separate quantum emitters, which lays the foundation of a scalable, photon-mediated quantum spin network[1]. With a specially designed spin-photon interface, the exciton spin could be coupled to the propagation direction of the photons scattered from the...
High quality single photon sources (SPSs) are extremely desirable in quantum information processing. In order to facilitate integration with existing silica fiber based photonic infrastructure, the SPS should emit photons in telecom spectral range where dispersion and propagation losses are the lowest. Such SPS can be realized in InAsP/InP quantum dot (QD) nanowires (NWs). Tailoring the NW...
Solid-state quantum emitters, particularly semiconductor quantum dots, are promising photon sources for quantum technologies. However, their interaction with phonons dampen the Rabi oscillations under resonant driving, leading to reduced state preparation fidelities. The phonon spectral density, a quantity for the carrier-phonon interaction strength, is a non-monotonic function in energy. This...
The promising application of single-photon sources (SPS) in quantum communication and cryptography has driven significant advances in this field and the search for new active materials. Among various emitters, semiconductor quantum dots (QDs) are of particular interest due to their high-quality single-photon emission, high generation rates, low multi-photon emission probabilities, and...
A single quantum emitter coupled to an optical waveguide is a promising platform for realizing highly efficient non-linear light-matter interactions. By employing a tapered geometry, both the injection and collection efficiency of light to such systems can be enhanced to near-unity. In this study, we investigate light injection into tapered InP nanowires with embedded InAsP quantum dots (QDs)...
Photonic integrated circuits are applied on a broad range of technologies, from communication to computing and sensing. With the increasing interest on quantum technologies, quantum photonic integrated circuits became subjects of additional attention.
Several material platforms have been investigated, keeping in mind that the following elements are strictly necessary [1]: efficient sources of...
The investigation of semiconductor quantum dots (QDs) that can emit single photons directly in the wavelength range of existing fiber communication networks is of key interest in order to harness the quantum properties of photonic qubits for everyday applications. While the first big achievements in fabricating highly efficient quantum light sources and the generation of spin-photon or...
A single photon source is a key technology for realizing quantum information processing tasks such as quantum key distribution, linear optical quantum computing and measurement-based quantum computing (MBQC). Many of these tasks - including MBQC – require deterministic generation of identical single photons [1]. Quantum dots (QD) embedded within nanowires are promising candidates for the...
Quantum emitters in transition metal dichalcogenides (TMDs), such as WSe2, are promising sources of single photons for quantum technologies, where one qubit is encoded in the quantum state of a single photon. The layered nature of TMDs allows straightforward fabrication and seamless integration of the source with other photonic structures. However, both the total efficiency (defined as the...
From atomic physics, it is well known that an ensemble of indistinguishable quantum emitters can show intriguing cooperative emission effects like superradiance, which is due to coherent coupling of the emitters to their common electromagnetic environment. Entanglement between the emitters leads to the formation of a giant dipole and hence to a superextensive enhancement of light absorption...
We investigate trivalent thulium ions embedded in a lithium niobate crystal (Tm$^{3+}$:LiNbO$_3$) as a platform for quantum information applications, including single and entangled photon sources, quantum memories, and quantum gates.
For this, we consider three infrared zero-phonon lines in (Tm$^{3+}$:LiNbO$_3$), corresponding to wavelengths of 795 nm, 1450 nm, and 1765 nm. We first...
Long-distance quantum communication can potentially suffer under decoherence of the photonic state in optical fibers. In comparison to polarization entanglement, time-bin entanglement is remarkably robust in fibers, which is an essential property for the implementation and usage of long-distance quantum information protocols such as quantum key distribution. In time-bin entanglement, the...
Frequency and time-resolved photon correlations [1] involve studying the photon statistics of a quantum source while considering both the detection times and the frequencies of emitted photons. In the case of a continuously driven two-level system, it is well-known that including the frequency of photons reveals a rich landscape of correlations beyond the expected antibunching behavior [2]....
Strain-free GaAs/AlGaAs semiconductor quantum dots (QDs) grown by droplet etching and nanohole infilling (DENI) are highly promising candidates for the on-demand generation of indistinguishable and entangled photon sources. The spectroscopic fingerprint and quantum optical properties of QDs are significantly influenced by their morphology. The effects of nanohole geometry and infilled material...
Cavity-enhanced diamond color-center qubits can be initialized, manipulated, entangled, and read individually with high fidelity, which makes this scheme ideal for implementing large-scale, modular quantum computers, quantum networks, and distributed quantum sensing systems [1 - 3]. However, the limited size of heteroepitaxially grown single-crystal diamond poses challenges for its integration...
The sequential resonant excitation of a 2-level quantum system results in the emission of a state of light showing time-entanglement encoded in the photon-number-basis. This notion can be extended to 3-level quantum systems as discussed in a recent proposal by Santoe et al. In this work, we report the experimental implementation of a sequential two-photon resonant excitation process of a...
We present our recent work in realizing fiber-pigtailed quantum light sources based on Purcell-enhanced semiconductor quantum dot (QD) emission in a hybrid circular Bragg grating (hCBG) cavity.
We employ a deterministic QD integration-method resulting in experimentally observed Purcell enhancement of >25, corresponding to <30 ps QD lifetimes. We show the direct effect of the strongly reduced...
This study presents an EOM-free method for generating 2-photon states using stimulated Two Photon Excitation (sTPE) in quantum dots. Following biexciton state generation, a second laser pulse (stimulation) stimulates the biexciton to the exciton state, with emission polarization controlled by this stimulation pulse. Sequential horizontal (H) and vertical (V) stimulation laser pulses result in...
Single-photon sources emitting at telecom wavelengths are a key component for applications of quantum information science. However, currently some of the best available single-photon sources are based on InAs/GaAs quantum dots, emitting at around 900nm. Nevertheless, quantum frequency conversion can be used to obtain photons at 1550nm, while maintaining high purity and photon...
In the development of photonic quantum networks [1], a crucial role will be played by the sources of entangled and single photons. Among the different possible candidates for this role, semiconductor quantum dots [2] are one of the most promising: They can emit single and entangle photons with on-demand operation, with intrinsically low multi-photon probability [3], high indistinguishability...
Semiconductor quantum dots, with their capability of confining charge carriers and various spin configurations resulting from it, can be regarded as a highly versatile platform for generating non-classical
light. While the generation of single photons or entangled photon pairs from quantum dots utilizes the so- called bright excitons and biexcitons respectively, quantum dots can also host...
