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Guang-Can Guo

Publications and source records attributed to Guang-Can Guo.

At least 1,009 records · Page 56Linked to original sources
arXiv1999

Probabilistic teleportation and entanglement matching

Teleportation may be taken as sending and extracting quantum information through quantum channels. In this report, it is shown that to get the maximal probability of exact teleportation through partially entangled quantum channels, the sender (Alice) need only to operate a measurement which satisfy an ``entanglement matching'' to this channel. An optimal strategy is also provided for the receiver (Bob) to extract the quantum information by adopting general evolutions.

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arXiv1999

General Strategies for Discrimination of Quantum States

We derive general discrimination of quantum states chosen from a certain set, given initial $M$ copies of each state, and obtain the matrix inequality, which describe the bound between the maximum probability of correctly determining and that of error. The former works are special cases of our results.

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arXiv1998

Quantum error avoiding codes versus quantum error correcting codes

A general theory of quantum error avoiding codes is established, and new light is shed on the relation between quantum error avoiding and correcting codes. Quantum error avoiding codes are found to be a special type of highly degenerate quantum error correcting codes. A combination of the ideas of correcting and avoiding quantum errors may yield better codes. We give a practical example.

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arXiv1998

Pulse controlled noise suppressed quantum computation

To make arbitrarily accurate quantum computation possible, practical realization of quantum computers will require suppressing noise in quantum memory and gate operations to make it below a threshold value. A scheme based on realistic quantum computer models is described for suppressing noise in quantum computation without the cost of stringent quantum computing resources.

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arXiv1998

Probabilistic cloning and identification of linearly independent quantum states

We construct a probabilistic quantum cloning machine by a general unitary-reduction operation. With a postselection of the measurement results, the machine yields faithful copies of the input states. It is shown that the states secretly chosen from a certain set $\$=\left\{\left| Ψ_1\right> ,\left| Ψ_2\right> ,... ,\left| Ψ_n\right> \right\} $ can be probabilistically cloned if and only if $% \left| Ψ_1\right>$, $\left| Ψ_2\right>$, $... ,$ and $\left| Ψ_n\right>$ are linearly-independent. We derive the best possible cloning efficiencies. Probabilistic cloning has close connection with the problem of identification of a set of states, which is a type of $n+1$ outcome measurement on $n$ linearly independent states. The optimal efficiencies for this type of measurement are obtained.

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arXiv1998

Optimal quantum codes for preventing collective amplitude damping

Collective decoherence is possible if the departure between quantum bits is smaller than the effective wave length of the noise field. Collectivity in the decoherence helps us to devise more efficient quantum codes. We present a class of optimal quantum codes for preventing collective amplitude damping to a reservoir at zero temperature. It is shown that two qubits are enough to protect one bit quantum information, and approximately $L+ 1/2 \log_2((πL)/2)$ qubits are enough to protect $L$ qubit information when $L$ is large. For preventing collective amplitude damping, these codes are much more efficient than the previously-discovered quantum error correcting or avoiding codes.

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arXiv1998

Perturbative expansions for the fidelities and spatially correlated dissipation of quantum bits

We construct generally applicable short-time perturbative expansions for some fidelities, such as the input-output fidelity, the entanglement fidelity, and the average fidelity. Successive terms of these expansions yield characteristic times for the damping of the fidelities involving successive powers of the Hamiltonian. The second-order results, which represent the damping rates of the fidelities, are extensively discussed. As an interesting application of these expansions, we use them to study the spatially-correlated dissipation of quantum bits. Spatial correlations in the dissipation are described by a correlation function. Explicit conditions are derived for independent decoherence and for collective decoherence.

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arXiv1998

Alternative approach to electromagnetic field quantization in nonlinear and inhomogeneous media

A simple approach is proposed for the quantization of the electromagnetic field in nonlinear and inhomogeneous media. Given the dielectric function and nonlinear susceptibilities, the Hamiltonian of the electromagnetic field is determined completely by this quantization method. From Heisenberg's equations we derive Maxwell's equations for the field operators. When the nonlinearity goes to zero, this quantization method returns to the generalized canonical quantization procedure for linear inhomogeneous media [Phys. Rev. A, 43, 467, 1991]. The explicit Hamiltonians for the second-order and third-order nonlinear quasi-steady-state processes are obtained based on this quantization procedure.

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arXiv1998

Reducing decoherence in quantum computer memory with all quantum bits coupling to the same environment

Decoherence in quantum computer memory due to the inevitable coupling to the external environment is examined. We take the assumption that all quantum bits (qubits) interact with the same environment rather than the assumption of separate environments for different qubits. It is found that the qubits are decohered collectively. For some kinds of entangled input states, no decoherence occurs at all in the memory even if the qubits are interacting with the environment. Based on this phenomenon, a scheme is proposed for reducing the collective decoherence. We also discuss possible implications of this decoherence model for quantum measurements.

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arXiv1997

Prevention of dissipation with two particles

An error prevention procedure based on two-particle encoding is proposed for protecting an arbitrary unknown quantum state from dissipation, such as phase damping and amplitude damping. The schemes, which exhibits manifestation of the quantum Zeno effect, is effective whether quantum bits are decohered independently or cooperatively. We derive the working condition of the scheme and argue that this procedure has feasible practical implementation.

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arXiv1997

Reply to the comment "quant-ph/9710002"

In the comment, Zanardi and Rasetti argue that several claims in our recent letter (Phys. Rev. Lett. 79, 1953, 1997) are questionable. The reply shows these claims remain true.

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arXiv1997

Preserving coherence in quantum computation by pairing quantum bits

A scheme is proposed for protecting quantum states from both independent decoherence and cooperative decoherence. The scheme operates by pairing each qubit (two-state quantum system) with an ancilla qubit and by encoding the states of the qubits into the corresponding coherence-preserving states of the qubit-pairs. In this scheme, the amplitude damping (loss of energy) is prevented as well as the phase damping (dephasing) by a strategy called the free-Hamiltonian-elimination We further extend the scheme to include quantum gate operations and show that loss and decoherence during the gate operations can also be prevented.

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arXiv1997

Ghost interference and diffraction based on the beam splitter

A simple scheme is proposed for observing the ghost interference and diffraction. The signal and the idler beams are produced by a beam splitter with the incident light being in a thermal state. A slit is inserted into the signal beam. We derive rigorously that interference-diffraction patterns can be observed in the first-order correlation by scanning the probe in the idler beam.

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arXiv1997

Correlations in interference and diffraction

Quantum formalism of Fraunhofer diffraction is obtained. The state of the diffraction optical field is connected with the state of the incident optical field by a diffraction factor. Based on this formalism, correlations of the diffraction modes are calculated with different kinds of incident optical fields. Influence of correlations of the incident modes on the diffraction pattern is analyzed and an explanation of the ''ghost'' diffraction is proposed.

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arXiv1997

Linearly-independent quantum states can be cloned

A fundamental question in quantum mechanics is, whether it is possible to replicate an arbitrary unknown quantum state. Then famous quantum no-cloning theorem [Nature 299, 802 (1982)] says no to the question. But it leaves open the following question: If the state is not arbitrary, but secretly chosen from a certain set $\$={ | Ψ_1> ,| Ψ_2> ,... ,| Ψ_n> } $, whether is the cloning possible? This question is of great practical significance because of its applications in quantum information theory. If the states $| Ψ_1>, | Ψ_2>,...$ and $| Ψ_n> $ are linearly-dependent, similar to the proof of the no-cloning theorem, the linearity of quantum mechanics forbids such replication. In this paper, we show that, if the states $| Ψ_1>, | Ψ_2>, ...$ and $| Ψ_n> $ are linearly-independent, they do can be cloned by a unitary-reduction process.

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arXiv1997

Two non-orthogonal states can be cloned by a unitary-reduction process

We show that, there are physical means for cloning two non-orthogonal pure states which are secretly chosen from a certain set $% \$={ | Ψ_0 > , | Ψ_1 > }$. The states are cloned through a unitary evolution together with a measurement. The cloning efficiency can not attain 100%. With some negative measurement results, the cloning fails.

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