Learning algorithm and application of quantum BP neural networks based on universal quantum gates

A quantum BP neural networks model with learning algorithm is proposed. First, based on the universality of single qubit rotation gate and two-qubit controlled-NOT gate, a quantum neuron model is constructed, which is composed of input, phase rotation, aggregation, reversal rotation and output. In this model, the input is described by qubits, and the output is given by the probability of the state in which （1） is observed. The phase rotation and the reversal rotation are performed by the universal quantum gates. Secondly, the quantum BP neural networks model is constructed, in which the output layer and the hide layer are quantum neurons. With the application of the gradient descent algorithm, a learning algorithm of the model is proposed, and the continuity of the model is proved. It is shown that this model and algorithm are superior to the conventional BP networks in three aspects： convergence speed, convergence rate and robustness, by two application examples of pattern recognition and function approximation.

Full-Blind Delegating Private Quantum Computation

The delegating private quantum computation(DQC)protocol with the universal quantum gate set{X,Z,H,P,R,CNOT}was firstly proposed by Broadbent et al.[Broadbent(2015)],and then Tan et al.[Tan and Zhou(2017)]tried to put forward a half-blind DQC protocol(HDQC)with another universal set{H,P,CNOT,T}.However,the decryption circuit of Toffoli gate(i.e.T)is a little redundant,and Tan et al.’s protocol[Tan and Zhou(2017)]exists the information leak.In addition,both of these two protocols just focus on the blindness of data(i.e.the client’s input and output),but do not consider the blindness of computation(i.e.the delegated quantum operation).For solving these problems,we propose a full-blind DQC protocol(FDQC)with quantum gate set{H,P,CNOT,T},where the desirable delegated quantum operation,one of{H,P,CNOT,T},is replaced by a fixed sequence(H,P,CZ,CNOT,T)to make the computation blind,and the decryption circuit of Toffoli gate is also optimized.Analysis shows that our protocol can not only correctly perform any delegated quantum computation,but also holds the characteristics of data blindness and computation blindness.

Anisotropic Spin Cluster as a Qubit

We study an anisotropic spin cluster of 3 spin S=1/2 particles with antiferromagnetic exchange interactionwith non-uniform coupling constants.A time-dependent magnetic field is applied to control the time evolution of thecluster.It is well known that for an odd number of sites a spin cluster qubit can be defined in terms of the ground statedoublet.The universal one-qubit logic gate can be constructed from the time evolution operator of the non-autonomousmany-body system,and the six basic one-qubit gates can be realized by adjusting the applied time-dependent magneticfield.

<i>C</i>¹²- <i>C</i>¹³Diamond Quantum Computer with Longitudinal rf-Magnetic Field

In the diamond C12 (nuclear spin zero) structure with a linear chain of C13 (nuclear spin one half) atoms is applied to a transverse static field with respect of this linear chain, having a gradient along the linear chain, and it is also applied to an rf-magnetic field in a plane with a component in the direction of the static field. It is shown that one qubit rotation, the Controlled-Not (CNOT), the Controlled-Controlled-NoT (CCNOT) quantum gates, and teleportation algorithm can be implemented on this structure using integer multiples of electromagnetic π-pulses. Therefore, a quantum computer can be constructed in this form.

Function synthesis algorithm based on RTD-based three-variable universal logic gates

Compared with complementary metal–oxide semiconductor(CMOS), the resonant tunneling device(RTD) has better performances; it is the most promising candidate for next-generation integrated circuit devices. The universal logic gate is an important unit circuit because of its powerful logic function, but there are few function synthesis algorithms that can implement an n-variable logical function by RTD-based universal logic gates. In this paper, we propose a new concept, i.e., the truth value matrix. With it a novel disjunctive decomposition algorithm can be used to decompose an arbitrary n-variable logical function into three-variable subset functions. On this basis, a novel function synthesis algorithm is proposed, which can implement arbitrary n-variable logical functions by RTD-based universal threshold logic gates(UTLGs), RTD-based three-variable XOR gates(XOR3s), and RTD-based three-variable universal logic gate(ULG3s). When this proposed function synthesis algorithm is used to implement an n-variable logical function, if the function is a directly disjunctive decomposition one, the circuit structure will be very simple, and if the function is a non-directly disjunctive decomposition one, the circuit structure will be simpler than when using only UTLGs or ULG3s. The proposed function synthesis algorithm is straightforward to program, and with this algorithm it is convenient to implement an arbitrary n-variable logical function by RTD-based universal logic gates.

Operational effects of the UNOT gate on classical and quantum correlations

The NOT gate that flips a classical bit is ubiquitous in classical information processing.However its quantum analogue,the universal NOT(UNOT) gate that flips a quantum spin in any alignment into its antipodal counterpart is strictly forbidden.Here we explore the connection between this discrepancy and how UNOT gates affect classical and quantum correlations.We show that while a UNOT gate always preserves classical correlations between two spins,it can non-locally increase or decrease their shared discord in ways that allow violation of the data processing inequality.We experimentally illustrate this using a multi-level trapped ^(171)Yb^+ ion that allows simulation of anti-unitary operations.

Design of a novel RTD-based three-variable universal logic gate

Traditional CMOS technology faces some fundamental physical limitations. Therefore, it has become very important for the integrated circuit industry to continue to develop modem devices and new design methods. The threshold logic gate has attracted much attention because of its powerful logic function. The resonant tunneling diode （RTD） is well suited for imple- menting the threshold logic gate because of its high-speed switching capability, negative differential resistance （NDR） charac- teristic, and functional versatility. In this paper, based on the Reed-Muller （RM） algebraic system, a novel method is proposed to convert three-variable non-threshold functions to the XOR of multiple threshold functions, which is simple and has a program- mable implementation. With this approach, all three-variable non-threshold functions can be presented by the XOR of two threshold functions, except for two special functions. On this basis, a novel three-variable universal logic gate （ULG3） is proposed, composed of two RTD-based universal threshold logic gates （UTLG） and an RTD-based three-variable XOR gate （XOR3）. The ULG3 has a simple structure, and a simple method is presented to implement all three-variable functions using one ULG3. Thus, the proposed ULG3 provides a new efficient universal logic gate to implement RTD-based arbitrary n-variable functions.

Programmable quantum processor implemented with superconducting circuit

A quantum processor might execute certain computational tasks exponentially faster than a classical processor.Here,using superconducting quantum circuits we design a powerful universal quantum processor with the structure of symmetric all-to-all capacitive connection.We present the Hamiltonian and use it to demonstrate a full set of qubit operations needed in the programmable universal quantum computations.With the device the unwanted crosstalk and ZZ-type couplings between qubits can be effectively suppressed by tuning gate voltages,and the design allows efficient and high-quality couplings of qubits.Within available technology,the scheme may enable a practical programmable universal quantum computer.

Investigation of Geiger-mode detector in multi-hit model for laser ranging

The performance of detector limits the overall performance of laser ranging system. And the design of multi-hit detector is one of the feasible ways to promote the performance of detector. Currently, the segmentation method or the recursive method is commonly used to analyze the multi-hit detector model. To the best of our knowledge, this paper is the first to propose a combinatorial method to solve the multi-hit detector model from the perspective of discrete time. Then, universal formulas of total signal detection probability and the average count are deduced based on the Poisson distribution signal. Furthermore, analysis is made to figure out how the average count changes with different parameters, such as the dead time, gating time, rate intensity. As a result, for GM-APD, the multi-hit detector model is verified advantageously compared to the single-hit detector model in improving the average count theoretically. Meanwhile, a discrete step feature is presented when average count changes with dead time or the gating time, which is of great significance in gating time optimization.

Universal quantum computation with qudits

Quantum circuit model has been widely explored for various quantum applications such as Shors algorithm and Grovers searching algorithm.Most of previous algorithms are based on the qubit systems.Herein a proposal for a universal circuit is given based on the qudit system,which is larger and can store more information.In order to prove its universality for quantum applications,an explicit set of one-qudit and two-qudit gates is provided for the universal qudit computation.The one-qudit gates are general rotation for each two-dimensional subspace while the two-qudit gates are their controlled extensions.In comparison to previous quantum qudit logical gates,each primitive qudit gate is only dependent on two free parameters and may be easily implemented.In experimental implementation,multilevel ions with the linear ion trap model are used to build the qudit systems and use the coupling of neighbored levels for qudit gates.The controlled qudit gates may be realized with the interactions of internal and external coordinates of the ion.