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Register a new userPurification of Single Photons from Room-Temperature Quantum Dots
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Single photon emitters are indispensable to photonic quantum technologies. Here we demonstrate waveform-controlled high-purity single photons from room-temperature colloidal quantum dots. The purity of the single photons does not vary with the excitation power, thereby allowing the generation rate to be increased without compromising the single-photon quality.
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We demonstrate and characterize interference between discrete photons emitted by two separate semiconductor quantum dot states in different samples excited by a pulsed laser. Their energies are tuned into resonance using strain. The photons have a total coalescence probability of 18.1% and the coincidence rate is below the classical limit. Post-selection of coincidences within a narrow time window increases the coalescence probability to 47%. The probabilities are reduced from unity because of dephasing and the postselection value is also reduced by the detector time response.
In the field of condensed matter, graphene plays a central role as an emerging material for nanoelectronics. Nevertheless, graphene is a semimetal, which constitutes a severe limitation for some future applications. Therefore, a lot of efforts are being made to develop semiconductor materials whose structure is compatible with the graphene lattice. In this perspective, little pieces of graphene represent a promising alternative. In particular, their electronic, optical and spin properties can be in principle controlled by designing their size, shape and edges. As an example, graphene nanoribbons with zigzag edges have localized spin polarized states. Likewise, singlet-triplet energy splitting can be chosen by designing the structure of graphene quantum dots. Moreover, bottom-up molecular synthesis put these potentialities at our fingertips. Here, we report on a single emitter study that directly addresses the intrinsic properties of a single graphene quantum dot. In particular, we show that graphene quantum dots emit single photons at room temperature with a high purity, a high brightness and a good photostability. These results pave the way to the development of new quantum systems based on these nanoscale pieces of graphene.
Efficient, high rate photon sources with high single photon purity are essential ingredients for quantum technologies. Single photon sources based on solid state emitters such as quantum dots are very advantageous for integrated photonic circuits, but they can suffer from a high two-photon emission probability, which in cases of non-cryogenic environment cannot be spectrally filtered. Here we propose two temporal purification-by-heralding methods for using a two photon emission process to yield highly pure and efficient single photon emission, bypassing the inherent problem of spectrally overlapping bi-photon emission. We experimentally demonstrate their feasibility on the emission from a single nanocrystal quantum dot, exhibiting single photon purities exceeding 99.5%, without a significant loss of single photon efficiency. These methods can be applied for any indeterministic source of spectrally broadband photon pairs.
Photonics is a promising platform for quantum technologies. However, photon sources and two-photon gates currently only operate probabilistically. Large-scale photonic processing will therefore be impossible without a multiplexing strategy to actively select successful events. High time-bandwidth-product quantum memories - devices that store and retrieve single photons on-demand - provide an efficient remedy via active synchronisation. Here we interface a GHz-bandwidth heralded single-photon source and a room-temperature Raman memory with a time-bandwidth product exceeding 1000. We store heralded single photons and observe a clear influence of the input photon statistics on the retrieved light, which agrees with our theoretical model. The preservation of the stored fields statistics is limited by four-wave-mixing noise, which we identify as the key remaining challenge in the development of practical memories for scalable photonic information processing.
Generation and manipulation of the quantum state of a single photon is at the heart of many quantum information protocols. There has been growing interest in using phase modulators as quantum optics devices that preserve coherence. In this Letter, we have used an electro-optic phase modulator to shape the state vector of single photons emitted by a quantum dot to generate new frequency components (modes) and explicitly demonstrate that the phase modulation process agrees with the theoretical prediction at a single photon level. Through two-photon interference measurements we show that for an output consisting of three modes (the original mode and two sidebands), the indistinguishability of the mode engineered photon, measured through the secondorder intensity correlation (g2(0)) is preserved. This work demonstrates a robust means to generate a photonic qubit or more complex state (e.g., a qutrit) for quantum communication applications by encoding information in the sidebands without the loss of coherence.
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