Quantum key distribution (QKD) allows the sharing of secret cryptographic keys between two distant users, whose intrinsic security is guaranteed by the laws of nature. Nowadays, the most promising technique for the integration of QKD in already deployed long-haul telecommunication fiber networks is the Twin-field QKD (TF-QKD) protocol, but it requires that the communication channel is stable in terms of phase oscillations and it is free from background light, that reduces the transmission key-rate. Recently, we presented a solution to the phase stabilization problem, derived from atomic clocks comparison technology, demonstrating advantages in performances of real word TF-QKD. Here we quantify and characterize the background photons, analyzing in details their effects on the transmission and the practicalities to reduce their contribution to a negligible level.
Nowadays, a technological challenge is to integrate quantum key distribution (QKD) protocols in already present telecommunication fiber networks. Twin-field QKD is one of the most promising techniques on long distances, but requires stabilizing the optical length of the communication channels between parties. Adapting interferometry techniques derived from frequency metrology, we developed a solution for the simultaneous key sharing and channel length control, and we demonstrated it on a 206 km field-deployed fiber with 65 dB loss. Our method reduces the quantum-bit-error-rate contributed by channel length variations to <1%, representing an effective solution for real-world quantum communications.
Weak value measurements have been a real breakthrough in the quantum measurement framework. In particular, quantum measurements may take advantage by anomalous weak values, i.e. values out of the eigenvalues spectrum of the measured observable, both for implementing new measurement techniques and studying Quantum Mechanics foundations. In this report we show three experiments with single photons presenting anomalous weak values: the first one tests the incompatibility between quantum mechanics and noncontextual hidden variables theories, the second one is the first realization of a sequential weak value evaluation of two incompatible observables on the same photon, and the last one shows how sequential weak values can be used to test Leggett-Garg inequalities extended to multiple-measurements scenarios.
In quantum mechanics, the eigenvalues and their corresponding probabilities specify the expectation value of a physical observable, which is known to be a statistical property related to large ensembles of particles. In contrast to this paradigm, we demonstrate a unique method allowing to extract the expectation value of a single particle, namely, the polarisation of a single protected photon, with a single experiment. This is the first realisation of quantum protective measurements.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.