Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:quant-ph/0404152 · Physical Review A

Optimal state encoding for quantum walks and quantum communication over spin systems

Henry L. Haselgrove

Published Dec 20, 2005• 77 citations
arXivHTMLPDF

Abstract

Recent work has shown that a simple chain of interacting spins can be used as a medium for high-fidelity quantum communication. We describe a scheme for quantum communication using a spin system that conserves $z$ spin, but otherwise is arbitrary. The sender and receiver are assumed to directly control several spins each, with the sender encoding the message state onto the larger state space of her control spins. Given that the encoding for the ``zero'' message basis state is chosen to be the all-spin-down state, we show how to find the encoding for the ``one'' basis state that maximizes the fidelity of communication, using a simple method based on the singular-value decomposition. Also, we show that this solution can be used to increase communication fidelity in a rather different circumstance: where no encoding of initial states is used, but where the sender and receiver control exactly two spins each and vary the interactions on those spins over time. The methods presented are computationally efficient, and numerical examples are given for systems having up to 300 spins.

DOI
10.1103/physreva.72.062326

Related papers

Optimized quantum state transfer through an XY spin chain

Yang Liu, Dong Zhou

Quantum state transfer along a one-dimensional spin chain has become a fundamental ingredient for quantum communication between distant nodes in a quantum network. We study the average fidelity of quantum state transfer (QST) along an $XY$ spin chain by adjusting the basis identification between the first spin and the last spin. In a proper choice of the basis identification, we find that the QST fidelity depends only on the average parity of the initial state linearly. We propose a simple scheme to adjust the basis identification to optimize the average fidelity such that it depends linearly on the absolute value of the average parity. In the case where the absolute value of the average parity is 1 we prove that the fidelity takes the maximum at any time over arbitrary initial state and basis identification.

arXiv:1312.0360•Physical Review A•Jun 26, 2014•11 citations

Spin-Chains as Quantum Channels for Qubit-State Transfer

Giulia Gualdi, Irene Marzoli, Paolo Tombesi

In this paper, we provide a simple strategy to optimize the performances of a spin chain as a quantum channel for state transfer.We investigate the most general conditions under which a long range interacting chain achieves the highest fidelity and the shortest transfer time. In this respect, we show that the symmetry of the spin chain plys a key role to identify the ideal system, which involves sender and receiver only, and provide numerical evidence. However, the two-spin ideal chain is unpractical due to the decrease of the coupling strength with distance. Therefore we show how to design a spin chain, which nearly approaches the optimal behaviour, while keeping the interaction strength still reasonably high.

International Conference on Quantum, Nano and Micro Technologies (ICQNM)•Feb 1, 2009•0 citations

Quantum Communication through an Unmodulated Spin Chain

Sougato Bose

We propose a scheme for using an unmodulated and unmeasured spin chain as a channel for short distance quantum communications. The state to be transmitted is placed on one spin of the chain and received later on a distant spin with some fidelity. We first obtain simple expressions for the fidelity of quantum state transfer and the amount of entanglement sharable between any two sites of an arbitrary Heisenberg ferromagnet using our scheme. We then apply this to the realizable case of an open ended chain with nearest neighbor interactions. The fidelity of quantum state transfer is obtained as an inverse discrete cosine transform and as a Bessel function series. We find that in a reasonable time, a qubit can be directly transmitted with better than classical fidelity across the full length of chains of up to 80 spins. Moreover, our channel allows distillable entanglement to be shared over arbitrary distances.

arXiv:quant-ph/0212041•Physical Review Letters•Nov 10, 2003•1,405 citations

Duplex quantum communication through a spin chain

Zhao-Ming Wang, C. Allen Bishop, Yongjian Gu +1 more

Data multiplexing within a quantum computer can allow for the simultaneous transfer of multiple streams of information over a shared medium thereby minimizing the number of channels needed for requisite data transmission. Here, we investigate a two-way quantum communication protocol using a spin chain placed in an external magnetic field. In our scheme, Alice and Bob each play the role of a sender and a receiver as two states, $\mathrm{cos}(\frac{{\ensuremath{\theta}}_{1}}{2})\left|0\right\ensuremath{\rangle}+\mathrm{sin}(\frac{{\ensuremath{\theta}}_{1}}{2}){e}^{i{\ensuremath{\varphi}}_{1}}\left|1\right\ensuremath{\rangle}$ and $\mathrm{cos}(\frac{{\ensuremath{\theta}}_{2}}{2})\left|0\right\ensuremath{\rangle}+\mathrm{sin}(\frac{{\ensuremath{\theta}}_{2}}{2}){e}^{i{\ensuremath{\varphi}}_{2}}\left|1\right\ensuremath{\rangle}$, are transferred through one channel simultaneously. We find that the transmission fidelity at each end of a spin chain can usually be enhanced by the presence of a second party. This is an important result for establishing the viability of duplex quantum communication through spin chain networks.

arXiv:1106.3502•Physical Review A•Aug 30, 2011•6 citations

Quantum entanglement in spin chains with the XY Hamiltonian at the quantum state transfer

E. I. Kuznetsova, I. D. Lazarev

In the present work the generation of entanglement between the receiver and sender is investigated in the process of the quantum state transfer in the homogeneous one-dimensional chain of spins 1/2 with the XY -Hamiltonian in the approximation of the nearest neighbour interactions. Fidelity is obtained for a quantum state transfer for various numbers of spins and temperatures and values of initial polarisation of the sender’s spin. The transmitted pure state is encoded in the state of first spin (sender) in the initial time moment. The other spins are in the thermodynamic equilibrium state. The reduced density matrix for the receiver and the sender is obtained for an investigation of entanglement in the “sender-receiver” system. The effect of temperature and polarization of the transmitted state on the generation of entanglement in the system is also investigated.

International Conference on Micro- and Nano-Electronics (ICMNE)•Mar 15, 2019•0 citations

Transfer of arbitrary two-qubit states via a spin chain

Salvatore Lorenzo, Tony J. G. Apollaro, Simone Paganelli +2 more

We investigate the fidelity of the quantum state transfer (QST) of two qubits by means of an arbitrary spin-$\frac{1}{2}$ network, on a lattice of any dimensionality. Under the assumptions that the network Hamiltonian preserves the magnetization and that a fully polarized initial state is taken for the lattice, we obtain a general formula for the average fidelity of the two qubits QST, linking it to the one- and two-particle transfer amplitudes of the spin excitations among the sites of the lattice. We then apply this formalism to a 1D spin chain with $XX$-Heisenberg type nearest-neighbour interactions adopting a protocol that is a generalization of the single qubit one proposed in Paganelli et al. [Phys. Rev. A 87, 062309 (2013)]. We find that a high-quality two qubit QST can be achieved provided one can control the local fields at sites near the sender and receiver. Under such conditions, we obtain an almost perfect transfer in a time that scales either linearly or, depending on the spin number, quadratically with the length of the chain.

arXiv:1502.02458•Physical Review A•Apr 16, 2015•56 citations
Recent work has shown that a simple chain of interacting spins can be used as a medium for high-fidelity quantum communication. We describe a scheme for quantum communication using a spin system that conserves zzz spin, but otherwise is arbitrary. The sender and receiver are assumed to directly control several spins each, with the sender encoding the message state onto the larger state space of her control spins. Given that the encoding for the zero'' message basis state is chosen to be the all-spin-down state, we show how to find the encoding for the one'' basis state that maximizes the fidelity of communication, using a simple method based on the singular-value decomposition. Also, we show that this solution can be used to increase communication fidelity in a rather different circumstance: where no encoding of initial states is used, but where the sender and receiver control exactly two spins each and vary the interactions on those spins over time. The methods presented are computationally efficient, and numerical examples are given for systems having up to 300 spins.
Quantum state transfer along a one-dimensional spin chain has become a fundamental ingredient for quantum communication between distant nodes in a quantum network. We study the average fidelity of quantum state transfer (QST) along an XYXYXY spin chain by adjusting the basis identification between the first spin and the last spin. In a proper choice of the basis identification, we find that the QST fidelity depends only on the average parity of the initial state linearly. We propose a simple scheme to adjust the basis identification to optimize the average fidelity such that it depends linearly on the absolute value of the average parity. In the case where the absolute value of the average parity is 1 we prove that the fidelity takes the maximum at any time over arbitrary initial state and basis identification.
In this paper, we provide a simple strategy to optimize the performances of a spin chain as a quantum channel for state transfer.We investigate the most general conditions under which a long range interacting chain achieves the highest fidelity and the shortest transfer time. In this respect, we show that the symmetry of the spin chain plys a key role to identify the ideal system, which involves sender and receiver only, and provide numerical evidence. However, the two-spin ideal chain is unpractical due to the decrease of the coupling strength with distance. Therefore we show how to design a spin chain, which nearly approaches the optimal behaviour, while keeping the interaction strength still reasonably high.
We propose a scheme for using an unmodulated and unmeasured spin chain as a channel for short distance quantum communications. The state to be transmitted is placed on one spin of the chain and received later on a distant spin with some fidelity. We first obtain simple expressions for the fidelity of quantum state transfer and the amount of entanglement sharable between any two sites of an arbitrary Heisenberg ferromagnet using our scheme. We then apply this to the realizable case of an open ended chain with nearest neighbor interactions. The fidelity of quantum state transfer is obtained as an inverse discrete cosine transform and as a Bessel function series. We find that in a reasonable time, a qubit can be directly transmitted with better than classical fidelity across the full length of chains of up to 80 spins. Moreover, our channel allows distillable entanglement to be shared over arbitrary distances.
Data multiplexing within a quantum computer can allow for the simultaneous transfer of multiple streams of information over a shared medium thereby minimizing the number of channels needed for requisite data transmission. Here, we investigate a two-way quantum communication protocol using a spin chain placed in an external magnetic field. In our scheme, Alice and Bob each play the role of a sender and a receiver as two states, $\mathrm{cos}(\frac{{\ensuremath{\theta}}_{1}}{2})\left|0\right\ensuremath{\rangle}+\mathrm{sin}(\frac{{\ensuremath{\theta}}_{1}}{2}){e}^{i{\ensuremath{\varphi}}_{1}}\left|1\right\ensuremath{\rangle}$ and $\mathrm{cos}(\frac{{\ensuremath{\theta}}_{2}}{2})\left|0\right\ensuremath{\rangle}+\mathrm{sin}(\frac{{\ensuremath{\theta}}_{2}}{2}){e}^{i{\ensuremath{\varphi}}_{2}}\left|1\right\ensuremath{\rangle}$, are transferred through one channel simultaneously. We find that the transmission fidelity at each end of a spin chain can usually be enhanced by the presence of a second party. This is an important result for establishing the viability of duplex quantum communication through spin chain networks.
In the present work the generation of entanglement between the receiver and sender is investigated in the process of the quantum state transfer in the homogeneous one-dimensional chain of spins 1/2 with the XY -Hamiltonian in the approximation of the nearest neighbour interactions. Fidelity is obtained for a quantum state transfer for various numbers of spins and temperatures and values of initial polarisation of the sender’s spin. The transmitted pure state is encoded in the state of first spin (sender) in the initial time moment. The other spins are in the thermodynamic equilibrium state. The reduced density matrix for the receiver and the sender is obtained for an investigation of entanglement in the “sender-receiver” system. The effect of temperature and polarization of the transmitted state on the generation of entanglement in the system is also investigated.
We investigate the fidelity of the quantum state transfer (QST) of two qubits by means of an arbitrary spin-12\frac{1}{2}21​ network, on a lattice of any dimensionality. Under the assumptions that the network Hamiltonian preserves the magnetization and that a fully polarized initial state is taken for the lattice, we obtain a general formula for the average fidelity of the two qubits QST, linking it to the one- and two-particle transfer amplitudes of the spin excitations among the sites of the lattice. We then apply this formalism to a 1D spin chain with XXXXXX-Heisenberg type nearest-neighbour interactions adopting a protocol that is a generalization of the single qubit one proposed in Paganelli et al. [Phys. Rev. A 87, 062309 (2013)]. We find that a high-quality two qubit QST can be achieved provided one can control the local fields at sites near the sender and receiver. Under such conditions, we obtain an almost perfect transfer in a time that scales either linearly or, depending on the spin number, quadratically with the length of the chain.