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Canadian Journal of Physics

Freezing the driven pulsed information of a single qubit

NASSER METWALLY, F. Al-Shawaikh, Saad S. M. Hassan

Published Feb 27, 2019• 1 citation
Publisher

Abstract

We use a rectangular pulse to freeze the possibility of estimating the coherent parameters (θ, [Formula: see text]) of a single qubit, the local information, and the fidelity of the driven qubit. The possibility of freezing these three quantities depends on the initial state settings and the strength of the pulse. It is shown that the freezing areas increase as the detuning increases, while they decrease at smaller values of the pulse strength. Moreover, as the Fisher information reaches its minimum bounds, the local information and the fidelity are maximized. We show that, when the Fisher information is completely frozen, the pulsed local information and the fidelity are frozen. The freezing degree depends on the initial detuning and the pulse strength. Our results show that, despite the initial and final states of the system being different, the amount of local information is independent of the initial state of the system. These results may be useful in the context of quantum cryptography, teleportation, and secure communication.

DOI
10.1139/cjp-2018-0651

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We use a rectangular pulse to freeze the possibility of estimating the coherent parameters (θ, [Formula: see text]) of a single qubit, the local information, and the fidelity of the driven qubit. The possibility of freezing these three quantities depends on the initial state settings and the strength of the pulse. It is shown that the freezing areas increase as the detuning increases, while they decrease at smaller values of the pulse strength. Moreover, as the Fisher information reaches its minimum bounds, the local information and the fidelity are maximized. We show that, when the Fisher information is completely frozen, the pulsed local information and the fidelity are frozen. The freezing degree depends on the initial detuning and the pulse strength. Our results show that, despite the initial and final states of the system being different, the amount of local information is independent of the initial state of the system. These results may be useful in the context of quantum cryptography, teleportation, and secure communication.
We use a rectangular pulse to freeze the possibility of estimating the coherent parameters (θ,ϕθ,ϕθ,ϕ) of a single qubit and the encoded information. It is shown that, as the possibility of estimating the parameters increases, the amount of encoded information decreases. The pulse strength and the detuning between the qubit and the pulse have a different effect on the estimation degree and the encoded information. We show that if the weight parameter, θθθ is estimated, the encoded information depends on the initial state settings. Meanwhile, the encoded information doesn't depend on the estimated phase parameter,ϕϕϕ. These results may be useful in the context of quantum cryptography, teleportation and secure communication.
Abstract We estimate the initial weight and phase parameters ( θ , ϕ ) of a single qubit system initially prepared in the coherent state | θ , ϕ 〉 and in interaction with three different shapes of pulses; rectangular, exponential, and sin 2 -pulses. In general, we show that the estimation degree of the weight parameter depends on the pulse shape and the initial phase angle, ( ϕ ) . For the rectangular pulse case, increasing the estimating rate of the weight parameter via the Fisher information function ( F θ ) is possible with small values of the atomic detuning parameter and larger values of pulse strength. Fisher information ( F ϕ ) increases suddenly at the resonant case to reach its maximum value if the initial phase ϕ = π / 2 and consequently one may estimate the phase parameter with a high degree of precision. If the initial system is coded with classical information, the upper bounds of Fisher information for resonant and non-resonant cases are much larger and consequently, one may estimate the phase parameter with a high degree of accuracy. Similarly, as the detuning increases the Fisher information decreases and therefore the possibility of estimating the phase parameter decreases. For exponential and sin 2 -pulses the Fisher information is maximum ( F θ , ϕ = 1 ) and consequently, one can always estimate the weight and the phase parameters ( θ , ϕ ) with a high degree of precision.
In this contribution, we introduce a technique to freeze the parameters which describe the accelerated states between two users to be used in the context of quantum cryptography and quantum teleportation. It is assumed that, the two users share different dimension sizes of particles, where we consider a qubit-qutrit system. This technique depends on local operations, where it is allowed that each particle interacts locally with a noisy phase channel. We show that, the possibility of freezing the information of quantum channel between the users depends on the initial state setting parameters, the initial acceleration parameter strength of the phase channel. It is shown that, one may increase the possibility of freezing the estimation degree of the parameters if only the larger dimension system or both particles pass through the noisy phase channel. Moreover, at small values of initial acceleration and large values of the channel strength, the size of freezing estimation areas increases. The results may be helpful in the context of quantum teleportation and quantum coding.
The Quantum Fisher information (QFI) of a two charged qubits system that interacts locally with a dephasing channel is quantified with respect to the charged qubits’ and the channel’s parameters. The behavior of Fisher information displays different phenomena as; the sudden changes (increasing/decreasing); the gradual decay and freezing of the QFI. It is shown that the QFI of the dephasing parameter decays gradually and vanishes completely as one increases the initial energies of the qubits and their mutual energy. The possibility of estimating the charged qubits’ energies may be maximized at smaller values of the initial dephasing’s parameter. The estimation degree of the mutual information reaches its upper bounds by increasing the initial energies. It is depicted that, by controlling the qubits’ and the channel’s parameters, the QFI may be frozen. We expect that this result may be interesting in the context of quantum encoding and quantum cryptography.
We investigate the transfer and exchange information between a single qubit system excited by a rectangular pulse. The dynamics of the system is treated within and outside rotating wave approximation (RWA). The initial state of the qubit plays an important role for sending information with high fidelity. Within RWA, and as the fidelity of the transformed information increases the exchange information with the environment increases. For increasing values of atomic detuning, the fidelity decreases faster and the exchange information has an upper limit. Outside RWA,the fidelity of the transformed information increases as one increases the perturbation parameter. However the exchange information is very high compared with that within RWA. The orthogonality speed of the travelling qubit is investigated for different classes of initial atomic state settings and field parameters.
Abstract The effects of noisy channels on the quantum Fisher information, channel capacity and non-local information of an accelerated qubit–qutrit system are discussed. Different phenomena are predicted for all these physical quantities, namely sudden/gradual and frozen behaviors. It is shown that the channel strength plays the central role in frozen behavior for all the noisy channels considered. The decay/increase rate depends on which subsystem is accelerated (qubit or qutrit). The frozen areas of these quantities are depicted at different ranges of channel strength and initial input. The maximum/minimum bounds of the estimation degree of the considered quantities depend on the used noisy channel and the dimensions of the accelerated subsystem.