We report the first experiment of continuous-variable measurement-device-independent quantum key distribution that enables secret key generation at a symbol rate of 5 MBaud without frequency and optical phase locking. This is achieved by using a new relay structure based on a polarization-based 90-degree optical hybrid and a well-designed DSP pipeline.
Certifying that quantum devices behave as intended is crucial for quantum information science. Here, methods are developed for certification of both state preparation devices and measurement devices based on prepare-and-measure experiments with independent devices. The experimenter assumes the independence of the devices and knowledge of the Hilbert space dimension. Thus no precise characterisation of any part of the experiment is required. The certification is based on a randomised version of unambiguous state discrimination and targets the class of state ensembles corresponding to quantum $t…
We study Bosonic representation of spin Ising model with the application of simulating two level systems using continuous variable quantum processors. We decompose the time evolution of spin systems into a sequence of continuous variable logical gates and analyze their structure. We provide an estimation of quantum circuit scaling with the size of the spin lattice system. Furthermore, we discuss the possibility of using a Gaussian Boson sampling device to estimate the ground state energy of Ising Hamiltonian. The result has potential application in developing hybrid classical-quantum algorithm…
Continuous-variable quantum information, encoded into infinite-dimensional quantum systems, is a promising platform for the realization of many quantum information protocols, including quantum computation, quantum metrology, quantum cryptography, and quantum communication. To successfully demonstrate these protocols, an essential step is the certification of multimode continuous-variable quantum states and quantum devices. This problem is well studied under the assumption that multiple uses of the same device result into identical and independently distributed (i.i.d.) operations. However, in …
Bell inequality can provide a useful witness for device-independent applications with quantum (or post-quantum) eavesdroppers. This feature holds only for single entangled systems. Our goal is to explore device-independent model for quantum networks. We firstly propose a Bell inequality to verify the genuinely multipartite nonlocality of connected quantum networks including cyclic networks and universal quantum computational resources for measurement-based computation model. This is further used to construct new monogamy relation in a fully device-independent model with multisource quantum res…
Randomness is a potential resource for cryptography, simulations and algorithms. Non-local correlations violating Bell's inequality certify the generation of bit strings whose randomness is guaranteed in a device-independent manner. We provide interesting semi-device independent randomness certification protocols by Kochen-Specker (KS) contextuality. For this, we first cast the Mermin's magic-square proof of KS contextuality for two-qubit system as a semi-device independent communication game in prepare-measure scenario. This provides a semi-device independent certification of two-bit of rando…
Measurement-device-independent quantum key distribution removes all detector-side attacks in quantum cryptography, and in the meantime doubles the secure distance. The source side, however, is still vulnerable to various attacks. In particular, the continuous phase randomization assumption on the source side is normally not fulfilled in experimental implementation and may potentially open a loophole. In this work, we first show that indeed there are loopholes for imperfect phase randomization in measurement-device-independent quantum key distribution by providing a concrete attack. Then we pro…
In this work, we develop upper bounds for key rates for device-independent quantum key distribution (DI-QKD) protocols and devices. We study the reduced cc-squashed entanglement and show that it is a convex functional. As a result, we show that the convex hull of the currently known bounds is a tighter upper bound on the device-independent key rates of standard CHSH-based protocol. We further provide tighter bounds for DI-QKD key rates achievable by any protocol applied to the CHSH-based device. This bound is based on reduced relative entropy of entanglement optimized over decompositions into …
Authentication of quantum sources is a crucial task in building reliable and efficient protocols for quantum-information processing. Steady progress vis-à-vis verification of quantum devices in the scenario with fully characterized measurement devices has been observed in recent years. When it comes to the scenario with uncharacterized measurements, the so-called black-box scenario, practical verification methods are still rather scarce. Development of self-testing methods is an important step forward, but these results so far have been used for reliable verification only by considering the as…
Recently, semi-device independent protocols have attracted increasing attention, guaranteeing security with few hypotheses and experimental simplicity. In this paper, we demonstrate a many-outcomes scheme with the binary phase-shift keying (BPSK) for a semi-device independent protocol based on the energy assumption. We show in theory that the number of certified random bits of the d-outcomes system outperforms the standard scheme (binary-outcomes). Furthermore, we compare the results of two well-known measurement schemes, homodyne and heterodyne detection. Lastly, taking into account the exper…
While it has recently been demonstrated how to certify the maximal amount of randomness from any pure two-qubit entangled state in a device-independent way [E. Woodhead et al., Phys. Rev. Research 2, 042028(R)(2020)], the problem of optimal randomness certification from entangled states of higher local dimension remains open. Here we introduce a method for device-independent certification of the maximal possible amount of $2\log_23$ random bits using pure bipartite entangled two-qutrit states and extremal nine-outcome general non-projective measurements. To this aim, we exploit the extended Be…
A semi-device-independent framework for prepare-and-measure experiments is introduced in which an experimenter can tune the degree of distrust in the performance of the quantum devices. In this framework, a receiver operates an uncharacterised measurement device and a sender operates a preparation device that emits states with a bounded fidelity with respect to a set of target states. No assumption on Hilbert space dimension is required. The set of quantum correlations is investigated and bounded from both the interior and the exterior. Furthermore, the optimal performance of quantum state dis…
We derive a device-independent quantum key distribution protocol based on synchronous correlations and their Bell inequalities. This protocol offers several advantages over other device-independent schemes including symmetry between the two users and no need for preshared randomness. We close a "synchronicity" loophole by showing that an almost synchronous correlation inherits the self-testing property of the associated synchronous correlation. We also pose a new security assumption that closes the "locality" (or "causality") loophole: an unbounded adversary with even a small uncertainty about…
Semi-device-independent randomness certification on discretized continuous-variable platforms
Federal University of Rio Grande do Norte(北里奥格兰德联邦大学);International Institute of Physics, Federal University of Rio Grande do Norte(北里奥格兰德联邦大学国际物理研究所);QuIIN - Quantum Industrial Innovation, EMBRAPII CIMATEC Competence Center in Quantum Technologies, SENAI CIMATEC(QuIIN量子工业创新,EMBRAPII CIMATEC量子技术能力中心,SENAI CIMATEC);Center for Macroscopic Quantum States bigQ, Department of Physics, Technical University of Denmark(丹麦技术大学宏观量子态bigQ研究中心)