Semiconductor quantum dots are prime candidates for quantum network applications such as quantum relays, but their typical emission wavelength, polarization qubit encoding scheme and low operating frequency are incompatible with existing technologies. Our work shows that InAs/InP quantum dots driven with GHz-clocked pulses, in combination with qubit transcoding interferometers, can bridge these gaps. The demonstrated teleportation of time-bin qubits in the telecom C band even when repetition rates exceed the inverse lifetime of the dot shows the potential for integrating such devices with long-distance quantum network technologies.
Quantum communication networks are formed of secure links, where information can be transmitted with security guaranteed by the quantum nature of light. An essential building block of such a network is a source of single photons and entangled photon pairs, compatible with the low-loss fibre telecom window around 1550 nm. Previous work based on semiconductor quantum dots (QDs), colour centres in diamond and single atoms has been limited by emission wavelengths unsuitable for long distance applications. Efforts have been made to use standard gallium arsenide based QDs by extending their operating wavelength range, however, electrically driven quantum light emission from quantum dots in this telecommunication window has not yet been demonstrated.
In this work, indium phosphide based QD devices have been developed to address this problem. The industry favoured growth method, metalorganic vapour phase epitaxy (MOVPE), has been used to create droplet QDs with low fine structure splitting (FSS). This growth scheme allows us to produce the first optoelectronic devices for single and entangled photon emission in the 1550 nm telecom window. We show single-photon emission with multi-photon events suppressed to 0.11±0.02. Furthermore, we obtain entangled light from the biexciton cascade with a maximum fidelity of 0.87± 0.04 which is sufficient for error correction protocols. We also show extended device operating temperature up to 93 K, allowing operation with liquid nitrogen or simple closed-cycle coolers. Our device can be directly integrated with existing long distance quantum communication, cryptography and quantum relay systems providing a new platform for developing quantum networks.
We implement the Bernstein-Vazirani algorithm on a 15-bit register encoding 215-1 elements using optics. The apparatus is efficient in that the physical size of the apparatus scales linearly with the size (i.e. number of digits) of the register. We demonstrate also that the algorithm may be performed not only without entanglement, as Meyer has indicated, but also with a computational basis that does not consist of orthogonal states, and that this coding is the source of the efficiency of the algorithm. This raises several questions: is this the only algorithm that makes use of these simplifying features, or do all quantum Oracles in fact require exponential resources for their construction?