A quantum federated learning framework for classical clients

Quantum federated learning(QFL)enables collaborative training of a quantum machine learning(QML)model among multiple clients possessing quantum computing capabilities,without the need to share their respective local data.However,the limited availability of quantum computing resources poses a challenge for each client to acquire quantum computing capabilities.This raises a natural question:Can quantum computing capabilities be deployed on the server instead?In this paper,we propose a QFL framework specifically designed for classical clients,referred to as CC-QFL,in response to this question.In each iteration,the collaborative training of the QML model is assisted by the shadow tomography technique,eliminating the need for quantum computing capabilities of clients.Specifically,the server constructs a classical representation of the QML model and transmits it to the clients.The clients encode their local data onto observables and use this classical representation to calculate local gradients.These local gradients are then utilized to update the parameters of the QML model.We evaluate the effectiveness of our framework through extensive numerical simulations using handwritten digit images from the MNIST dataset.Our framework provides valuable insights into QFL,particularly in scenarios where quantum computing resources are scarce.

Quantum private query: A new kind of practical quantum cryptographic protocol

This research aims to review the developments in the field of quantum private query(QPQ), a type of practical quantum cryptographic protocol. The primary protocol, as proposed by Jacobi et al., and the improvements in the protocol are introduced.Then, the advancements made in sability, theoretical security, and practical security are summarized. Additionally, we describe two new results concerning QPQ security. We emphasize that a procedure to detect outside adversaries is necessary for QPQ, as well as for other quantum secure computation protocols, and then briefly propose such a strategy. Furthermore, we show that the shift-and-addition or low-shift-and-addition technique can be used to obtain a secure real-world implementation of QPQ, where a weak coherent source is used instead of an ideal single-photon source.

A lattice-based signcryption scheme without random oracles

In order to achieve secure signcryption schemes in the quantum era, Li Fagen et al. [Concurrency and Computation： Practice and Experience, 2012, 25（4）： 2112-2122] and Wang Fenghe et al. [Applied Mathematics ＆ Information Sciences, 2012, 6（1）： 23-28] have independently extended the concept of signcryption to lattice-based cryptography. However, their schemes are only secure under the random or- acle model. In this paper, we present a lattice-based signcryp- tion scheme which is secure under the standard model. We prove that our scheme achieves indistinguishability against adaptive chosen-ciphertext attacks （IND-CCA2） under the learning with errors （LWE） assumption and existential unforgeability against adaptive chosen-message attacks （EUF- CMA） under the small integer solution （SIS） assumption.

Novel quantum circuit implementation of Advanced Encryption Standard with low costs

In this study, we examine how the quantum circuit of the Advanced Encryption Standard(AES) can be optimized from two aspects, i.e., number of qubits and T-depth. To reduce the number of qubits, we present three kinds of improved quantum circuits of S-box for different phases in the AES. We found that the number of qubits in the round function can be decreased by introducing the circuit sending |a> to |S(a)>. As a result, compared with the previous quantum circuits where 400/640/768 qubits are required,our circuits of AES-128/-192/-256 only require 270/334/398 qubits. To reduce the T-depth, we propose a new circuit of AES's S-box with a T-depth of 4. Accordingly, the T-depth of our AES-128/-192/-256 quantum circuits become 80/80/84 instead of120/120/126 in a previous study.

Quantum position verification in bounded-attack-frequencymodel

In 2011, Buhrman et al. proved that it is impossible to design an unconditionally secure quantum position verification(QPV)protocol if the adversaries are allowed to previously share unlimited entanglements. Afterwards, people started to design secure QPV protocols in practical settings, e.g. the bounded-storage model, where the adversaries' pre-shared entangled resources are supposed to be limited. Here we focus on another practical factor that it is very difficult for the adversaries to perform attack operations with unlimitedly high frequency. Concretely, we present a new kind of QPV protocols, called non-simultaneous QPV.And we prove the security of a specific non-simultaneous QPV protocol with the assumption that the frequency of the adversaries' attack operations is bounded, but no assumptions on their pre-shared entanglements or quantum storage. Actually, in our nonsimultaneous protocol, the information whether there comes a signal at present time is also a piece of command. It renders the adversaries "blind", that is, they have to execute attack operations with unlimitedly high frequency no matter whether a signal arrives, which implies the non-simultaneous QPV is also secure in the bounded-storage model.

Local discrimination scheme for some unitary operations

It has been shown that for two different multipartite unitary operations U_1 and U_2, when tr(U_1~?U_2) = 0, they can always be perfectly distinguished by local operations and classical communication in the single-run scenario. However, how to find the detailed scheme to complete the local discrimination is still a fascinating problem. In this paper, aiming at some U_1 and U_2 acting on the bipartite and tripartite space respectively, especially for U_1~?U_2 locally unitary equivalent to the high dimensional X-type hermitian unitary matrix V with trV = 0, we put forward the explicit local distinguishing schemes in the single-run scenario.