arXiv subjects

Xijia Miao

Publications and source records attributed to Xijia Miao.

At least 19 recordsLinked to original sources

arXiv2026

Subspace-selective unitary manipulation based on the Hilbert-space symmetric structures in the multiple-quantum operator algebra spaces in the quantum-computing speedup theory

The quantum-computing speedup theory considers the symmetric structures and properties of quantum systems as the fundamental Quantum-Computing-Speedup (QCS) resources which are responsible for exponentially speeding up quantum computing and simulating. At present a large and important problem is how to make use of the fundamental QCS resources to speed up essentially quantum computing and simulating. Here the author makes a great effort toward solving this important problem. The theoretical research work in this paper is mainly divided into the two Parts I and II. The Part I investigates mainly the multiple-quantum operator algebra spaces. And the relationships are analyzed among the multiple-quantum operator algebra spaces, quantum simulating for the unitary time-evolutional processes, and the fundamental QCS resources which exist in the different kinds of basic quantum spaces: the multiple-quantum operator algebra spaces, the density operator spaces, and the Hilbert spaces. It concludes that the multiple-quantum operator algebra space must be positioned as the central place where the fundamental QCS resources are exploited to speed up quantum computing and simulating. The Part II investigates mainly the subspace-selective unitary manipulation based on the Hilbert-space symmetric structures. Recognize that the multiple-quantum operator algebra space is the central place. Then those fundamental QCS resources original from the Hilbert space (a quantum-state space) must be explicitly taken into account in the multiple-quantum operator algebra space (a linear operator space). This is an important problem. The subspace-selective unitary manipulation is able to solve this problem. It aims to harness the fundamental QCS resources original from the Hilbert space to speed up quantum computing and simulating in the multiple-quantum operator algebra space.

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arXiv2020

The duality-character Solution-Information-Carrying (SIC) unitary propagators

The HSSS quantum search process owns the dual character that it obeys both the unitary quantum dynamics and the mathematical-logical principle of the unstructured search problem. It is essentially different from a conventional quantum search algorithm. It is constructed with the duality-character oracle operations of unstructured search problem. It consists of the two consecutive steps: (1) the search-space dynamical reduction and (2) the dynamical quantum-state-difference amplification (QUANSDAM). The QUANSDAM process is directly constructed with the SIC unitary propagators, while the latter each are prepared with the basic SIC unitary operators. Here the preparation for the SIC unitary propagators of a single-atom system is concretely carried out by starting from the basic SIC unitary operators. The SIC unitary propagator of a quantum system may reflect the quantum symmetry of the quantum system, while the basic SIC unitary operators may not. The quantum symmetry is considered as the fundamental quantum-computing-speedup resource in the quantum-computing speedup theory. The purpose for the preparation is ultimately to employ the quantum symmetry to speed up the QUANSDAM process. The preparation is a solution-information transfer process. It is unitary and deterministic. It obeys the information conservation law. In methodology it is based on the energy eigenfunction expansion and the multiple-quantum operator algebra space. Furthermore, a general theory mainly based on the Feynman path integration technique and also the energy eigenfunction expansion method is established to treat theoretically and calculate a SIC unitary propagator of any quantum system in the coordinate representation, which may be further used to construct theoretically an exponential QUANSDAM process in future.

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arXiv2016

The unitary dynamical state-locking process, the HSSS quantum search process, and the quantum-computing speedup theory

A unitary dynamical state-locking (UNIDYSLOCK) process is a unitary process that can transform two orthogonal states to two non-orthogonal states. Its inverse process, i.e., the QUANSDAM process could realize an exponential QC speedup in solving an unstructured search problem in the quantum-computing (QC) speedup theory (X. Miao, arXiv:1105.3573 [quant-ph] (2011)). In this paper the principle of how a UNIDYSLOCK process works is described on the basis of the QC speedup theory. A UNIDYSLOCK process does not exist at all in pure quantum mechanics. That it can change the quantum-state difference is original from the fundamental interaction between the quantum physical laws (i.e., the unitary quantum dynamics and the Hilbert-space symmetric structure) and the mathematical-logical principle of the search problem. It is characteristic for the QC speedup theory. Even if a usual quantum computational (Qc) process that is reversible or unitary contained a UNIDYSLOCK (or QUANSDAM) process, the contribution of the UNIDYSLOCK (or QUANSDAM) process to the QC speedup of the usual Qc process would be secondary or negligible. Whether or not a UNIDYSLOCK (or QUANSDAM) process can make an essential contribution to a QC speedup can distinguish the QC speedup theory from any usual Qc theory. In the paper the QC speedup mechanism of the HSSS quantum search process is also studied. The search process is essentially different from a usual quantum search algorithm. It works in both the usual Hilbert space and the math Hilbert space. Due to the math Hilbert space a mathematical-parallel operation is characteristic for the QC speedup theory, while a quantum-parallel operation is characteristic for the usual Qc theory. The fundamental interaction mentioned above and the fundamental quantum-computing resource play the main role in speeding up the search process.

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arXiv2013

Unitary manipulation of a single atom in time and space --- The spatially-selective and internal-state-selective triggering pulses

A spatially-selective and internal-state-selective triggering pulse is an important component to realize the unitary dynamical state-locking process which may be used to realize the reversible and unitary halting protocol and construct the unstructured quantum search process based on the tensor-product Hilbert-space symmetric structure and the unitary quantum dynamics. In this paper it is shown how a spatially-selective and internal-state-selective triggering pulse is constructed generally in the quantum system of a single atom. Rigorous theoretical calculation and error estimation, which are based on the Trotter-Suzuki decomposition method and the multiple-Gaussian-wave-packet expansion method, are carried out for the time evolution process of a single atom in the double-well potential field and in the presence of the spatially-selective and internal-state-selective triggering pulse. It proves that the spatially-selective and internal-state-selective triggering pulse is feasible, that is, the possible errors generated by the triggering pulse are shown to be controllable. This rigorous theoretical calculation also shows that the spatially-selective and internal-state-selective triggering pulse may be different from its corresponding ideal internal-state-selective triggering pulse that is not spatially selective, but the difference between their final states of the time evolution process is controllable. These computational results are achieved with the help of the Gaussian wave-packet motional states and the space-dependent quadratic Hamiltonians of a single atom. The methods and techniques developed in the paper are useful for studying the quantum-computing speedup mechanism of the unitary quantum dynamics in the quantum system of a single atom.

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arXiv2012

An explicit criterion for existence of the Magnus solution for a coupled spin system under a time-dependent radiofrequency pulse

The explicit criterion is derived in detail for the convergence of the Magnus expansion and the existence of the Magnus solution in the interaction picture, i.e., the exponential propagator in the weakly coupled spin (I=1/2) system SnAMX... (n=1,2,3,...) in which only spin group S is subjected to a time-dependent shaped selective radiofrequency pulse. The derivation is built on the same scheme as the Maricq's (J. Chem. Phys. 86 (1987) 5647). It is shown that the criterion depends only upon amplitude of the time-dependent field applied to the system, and the Magnus expansion converges and the Magnus solution exists when the flip angle of a non-negative-amplitude shaped RF pulse or a weak-amplitude shaped pulse is smaller than 2pi. The exponential propagator then can be decomposed into a product of a series of elementary propagators and can be used to determine time evolution of the spin system under the shaped pulse. The linear differential equations to determine the unknown parameters in the Magnus solution are obtained explicitly. An alternative propagator in an expansion form for the Magnus solution is also proposed to describe the time evolution when the criterion is not met.

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arXiv2011

The universal quantum driving force to speed up a quantum computation -- The unitary quantum dynamics

It is shown in the paper that the unitary quantum dynamics in quantum mechanics is the universal quantum driving force to speed up a quantum computation. This assertion supports strongly in theory that the unitary quantum dynamics is the fundamental and universal principle in nature. On the other hand, the symmetric structure of Hilbert space of a composite quantum system is the quantum-computing resource that is not owned by classical computation. A new quantum-computing speedup theory is set up on the basis of the unitary quantum dynamics. Both the unitary quantum dynamics and the symmetric structure and property of the Hilbert space of the quantum system are mainly responsible for an exponential quantum-computing speedup for a general efficient quantum algorithm. The inherent importance for the unitary quantum dynamics to speed up a quantum computation lies in the unique ability of the unitary quantum dynamics to build the effective interaction between the symmetric structure of the Hilbert space of the quantum system and the mathematical symmetric structure of a problem to be solved on the quantum system. This unique ability could result in an essential difference of computational power between quantum and classical computations by combining the symmetric structure and property of the Hilbert space. The new quantum-computing speedup theory also provides reasonable mechanisms for exponential quantum-computing speedup for the existing efficient quantum algorithms based on the quantum parallel principle. These existing quantum algorithms including the hidden-subgroup-problem quantum algorithms and conventional quantum search algorithms have the common character that the symmetric structure of the Hilbert space does not have any effective effect on these quantum algorithms. This could be the main reason why these quantum algorithms are quite special and considered to be semiclassical.

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arXiv2009

Introduction to the multiple-quantum operator spaces

The multiple-quantum NMR spectroscopy has an extensive application in determination of the bio-macro-molecular structures and in the investigation of the properties of a variety of physical materials. In quantum computation the multiple-quantum transition processes have been used to construct the quantum circuits, quantum algorithms, and quantum simulations. The multiple-quantum operator algebra spaces are closely related to the symmetries of a multiple-spin quantum system. They may have an important effect on the multiple-quantum transition processes and the multiple-quantum NMR spectroscopy of the spin system. Here gives a brief introduction to the multiple-quantum operator algebra spaces.

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arXiv2009

The STIRAP-based unitary decelerating and accelerating processes of a single free atom

A STIRAP-based unitary decelerating (accelerating) process consists of a train of the standard three-state STIRAP pulse sequences which may act as the basic unitary decelerating (accelerating) sequences. The present work is focused on investigating analytically and quantitatively how the momentum distribution of a momentum superposition state such as a momentum Gaussian wave-packet state of a single freely moving atom affects the STIRAP state transfer in these decelerating and accelerating processes. The complete STIRAP state transfer and the unitarity of these processes are stressed highly in the investigation. It has been shown that the momentum distribution has an important influence upon the STIRAP state-transfer efficiency. In the ideal adiabatic condition these unitary decelerating and accelerating processes for a freely moving atom are studied in detail, and it is shown that they can be used to manipulate and control in time and space the center-of-mass position and momentum of a Gaussian wave-packet motional state of a free atom. Two general (strict and accurate) adiabatic conditions for the basic STIRAP decelerating and accelerating processes are derived analytically. With the help of the STIRAP theory and the unitary quantum dynamics it confirms theoretically that the time- and space-compressing processes of the quantum control process (quant-ph/0607144) can be realized almost perfectly by the STIRAP-based unitary decelerating and accelerating processes in the ideal or nearly ideal adiabatic condition.

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arXiv2007

Unitarily manipulating in time and space a Gaussian wave-packet motional state of a single atom in a quadratic potential field

The paper first discusses theoretically the off-resonance selective excitation method that is dependent on the atomic internal states and used to generate approximately a standard coherent state of harmonic oscillator. The coherent average method then is proposed to construct the state-selective trigger pulse. A state-selective trigger pulse can keep Gaussian shape unchanged but change in an internal-state-dependent form the center-of-mass position and/or momentum of an atomic Gaussian wave-packet motional state. A Gaussian wave-packet state is one of the simplest wave-packet states that can be easily manipulated and controlled in time and space. The paper also investigates how to manipulate in time and space an atomic Gaussian wave-packet motional state by a generalized quadratic potential field. A general quadratic Hamiltonian can affect not only the center-of-mass position and momentum but also the complex linewidth of a Gaussian wave-packet motional state while keep Gaussian shape of the motional state unchanged. It is shown that generally quadratic terms of a quadratic Hamiltonian can control directly the complex linewidth, while linear terms of a quadratic Hamiltonian can affect only the center-of-mass position and momentum of a Gaussian wave-packet motional state.

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arXiv2006

The basic principles to construct a generalized state-locking pulse field and simulate efficiently the reversible and unitary halting protocol of a universal quantum computer

It has been shown (Arxiv: quant-ph/0507236) that a universal quantum computer could be powerful enough to solve efficiently the quantum search problem, and the reversible and unitary halting protocol based on the state-locking pulse field is the key component to construct the efficient quantum search processes, while the state-locking pulse field is the key component to generate the reversible and unitary halting protocol. In this paper the reversible and unitary halting protocol and the generalized state-locking pulse field have been extensively investigated theoretically. The basic principles to construct the state-locking pulse field and design the reversible and unitary halting protocol are studied in detail. A generalized state-locking pulse field is generally dependent upon the time and space variables. It could be a sequence of time- and space-dependent electromagnetic pulse fields and could also contain the time- and space-dependent potential fields. Thus, the reversible and unitary halting protocol built up out of the state-locking pulse field generally consists of a sequence of time- and space-dependent unitary evolution processes. It is shown how the quantum control process is constructed to simulate efficiently the reversible and unitary halting protocol. An improved subspace-reduction quantum program and circuit based on the reversible and unitary halting protocol is proposed as the key component to construct further an efficient quantum search process. A simple atomic physical system that is an atomic ion or a neutral atom in the double-well potential field is proposed to show how the state-locking pulse field is generated and how to implement the reversible and unitary halting protocol.

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arXiv2005

Quantum search processes in the cyclic group state spaces

The hardness to solve an unstructured quantum search problem by a standard quantum search algorithm mainly originates from the low efficiency to amplify the amplitude of the marked state by the oracle unitary operation associated with other known quantum operations. In order to bypass the square speedup limitation of a standard quantum search algorithm it is necessary to develop other type of quantum search algorithms. It is described in detail in the paper for a quantum dynamical method to solve the quantum search problems in the cyclic group state space. The binary dynamical representation for a quantum state in the Hilbert space of the n-qubit quantum system is generalized to the multi-base dynamical representation for a quantum state in the cyclic group state space. Thus, any quantum state in the cyclic group state space may be described completely in terms of a set of dynamical parameters that are closely related to the symmetric property and structure of the cyclic group. The quantum search problem therefore could be solved by determining the set of dynamical parameters that describe completely the unknown marked state of the search problem instead by directly measuring the marked state which is a necessary step in the standard quantum search algorithm. An unstructured quantum search problem in the Hilbert space is inevitably affected greatly by the symmetric property and structure of a group. The main attempt of the paper is to make use of the symmetric properties and structures of groups to help solving the quantum search problems in the group state spaces. It is shown how the quantum search process could be reduced from the cyclic group state space to these cyclic group state subspaces with the help of the symmetric property and structure of the cyclic group on a universal quantum computer.

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arXiv2004

Efficient multiple-quantum transition processes in an n-qubit spin system

The whole Hilbert state space of an n-qubit spin system can be divided into (n+1) state subspaces according to the angular momentum theory of quantum mechanics. Here it is shown that any unknown state in such a state subspace, whose dimensional size is proportional to either a polynomial or exponential function of the qubit number n, can be transferred efficiently into a larger subspace with a dimensional size generally proportional to an exponential function of the qubit number by the multiple-quantum unitary transformation with a subspace-selective multiple-quantum unitary operator. The efficient quantum circuits for the subspace-selective multiple-quantum unitary operators are really constructed.

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arXiv2003

A prime factorization based on quantum dynamics on a spin ensemble (I)

In this paper it has been described how to use the unitary dynamics of quantum mechanics to solve the prime factorization problem on a spin ensemble without any quantum entanglement. The ensemble quantum computation for the prime factorization is based on the basic principle that both a closed quantum system and its ensemble obey the same unitary dynamics of quantum mechanics if there is not any decoherence effect in both the quantum system and its ensemble. It uses the NMR multiple-quantum measurement techniques to output the quantum computational results that are the inphase multiple-quantum spectra of the spin ensemble. It has been shown that the inphase NMR multiple-quantum spectral intensities used to search for the period of the modular exponential function may reduce merely in a polynomial form as the qubit number of the spin ensemble. The time evolution process of the modular exponential operation on the quantum computer obeys the unitary dynamics of quantum mechanics and hence the computational output is governed by the quantum dynamics. This essential difference between the quantum computer and the classical one could be the key point for the quantum computation outperforming the classical one in the prime factorization on a spin ensemble without any quantum entanglement. It has been shown that the prime factorization based on the quantum dynamics on a spin ensemble is locally efficient at least. This supports the conjecture that the quantum dynamics could play an important role for the origin of power of quantum computation and quantum entanglement could not be a unique resource to achieve power of quantum computation in the prime factorization.

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arXiv2002

Solving the quantum search problem in polynomial time on an NMR quantum computer

The quantum search problem is an important problem due to the fact that a general NP problem can be solved efficiently by an unsorted quantum search algorithm. Here it has been shown that the quantum search problem could be solved in polynomial time on an NMR quantum computer. The NMR ensemble quantum computation is based on the quantum mechanical unitary dynamics that both a closed quantum system and its ensemble obey the same quantum mechanical unitary dynamics instead of on the pseudopure state or the effective pure state of the classical NMR quantum computation. Based on the new principle the conventional NMR multiple-quantum spectroscopy has been developed to solve experimentally the search problem. The solution information of the search problem is first loaded on the unitary evolution propagator which is constructed with the oracle unitary operation and oracle-independent unitary operations and is used to excite the multiple-quantum coherence in a spin ensemble. Then the multiple- quantum spectroscopy is used to extract experimentally the solution information. It has been discussed how to enhance the output NMR signal of the quantum search NMR multiple-quantum pulse sequence and some approaches to enhancing the NMR signal are also proposed. The present work could be helpful for conventional high field NMR machines to solve efficiently the quantum search problem.

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arXiv2002

Ultra-broadband Heteronuclear Hartmann-Hahn polarization transfer

It is showed on the basis of the multiple-quantum operator algebra space formalism that ultra-broadband heteronuclear Hartmann-Hahn polarization transfer could be achieved by the amplitude- and frequency-modulation quasi-adiabatic excitation (90 degree) pulses, while it is usually difficult for the adiabatic inversion pulses to achieve effectively broadband Hartmann-Hahn transfer in a heteronuclear coupled two-spin system. The adiabatic and quasi-adiabatic pulses have an important property that within their activation bandwidth flip angle of the pulses is independent of the pulse duration and the bandwidth increases as the pulse duration. This property is importanr for construction of the heteronuclear Hartmann-Hahn transfer sequences with the quasi-adiabatic 90 degree pulses. Theoretic analysis and numerical simulation show that the heteronuclear Hartmann-Hahn transfer is performed in the even-order multiple- quantum operator algebra subspace of the two-spin system. The multiple-quantum operator algebra space formalism may give a powerful guide to the construction of ultra- broadband heteronuclear Hartmann-Hahn transfer sequences with the quasi-adiabatic 90 degree pulses.

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arXiv2001

A polynomial-time solution to the parity problem on an NMR quantum computer

An efficient quantum algorithm is proposed to solve in polynomial time the parity problem, one of the hardest problems both in conventional quantum computation and in classical computation, on NMR quantum computers. It is based on the quantum parallelism principle in a quantum ensemble, the selective decoherence manipulation, and the NMR phase-sensitive measurement. The quantum circuit for the quantum algorithm is designed explicitly.

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arXiv2001

Universal construction for the unsorted quantum search algorithms

The multiple-quantum operator algebra formalism has been exploited to construct generally an unsorted quantum search algorithm. The exponential propagator and its corresponding effective Hamiltonian are constructed explicitly that describe in quantum mechanics the time evolution of a multi- particle two-state quantum system from the initial state to the output of the unsorted quantum search problem. The exponential propagator usually may not be compatible with the mathematical structure and principle of the search problem and hence is not a real quantum search network, but it can be further decomposed into a product of a series of the oracle unitary operations such as the selective phase-shift operations and the nonselective unitary operations which can be expressed further as a sequence of elementary building blocks such as one-qubit quantum gates and the two-qubit diagonal phase gates, resulting in that the decomposed propagator is compatible with the mathematical structure and principle of the search problem and thus, becomes a real quantum search network. The decomposition for the propagator can be achieved with the help of the operator algebra structure and symmetry of the effective Hamiltonian, and the properties of the multiple-quantum operator algebra spaces, especially the characteristic transformation behavior of the multiple-quantum operators under the z-axis rotations. It has been shown that the computational complexity of the search algorithm is dependent upon that of the numerical multidimensional integration and hence it is believed that the search algorithm could solve efficiently the unsorted search problem. An NMR device is also proposed to solve efficiently the unsorted search problem in polynomial time.

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arXiv2000

A convenient method to prepare the effective pure state in a quantum ensemble

A simple method is proposed to prepare conveniently the effective pure state |00...0><0...00| with any number of qubits in a quantum ensemble. The preparation is based on the temporal averaging (Knill, Chuang, and Laflamme, Phys.Rev.A 57, 3348(1998)). The quantum circuit to prepare the effective pure state is designed in a unified and systematical form and is explicitly decomposed completely into a product of a series of one-qubit quantum gates and the two-qubit diagonal quantum gates. The preparation could be programmed and implemented conveniently on an NMR quantum computer.

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