We investigate the parameter estimation problem in a two-qubit system, in which each qubit is independently interacting with its Markovian environment. We study in detail the sensitivity of the estimation on the decoherence rate $γ$ and the two-qubit interaction strength $v$ . In particular, the dynamics of quantum Fisher information are employed as a measure to quantify the precision of the estimations. We find that the quantum Fisher information with respect to the decoherence rate scales like $t^2/[\exp(γt)-1]$ and $\exp(-2γt)$ in the unitary limit and the completely decoherent limit, respectively. When we estimate the interaction strength $v$ , the quantum Fisher information shows oscillation behavior in term of time. In addition, our results provide further evidence that the entanglement of the input state may not enhance quantum metrology.We investigate the parameter estimation problem in a two-qubit system, in which each qubit is independently interacting with its Markovian environment. We study in detail the sensitivity of the estimation on the decoherence rate $γ$ and the two-qubit interaction strength $v$. In particular, the dynamics of quantum Fisher information are employed as a measure to quantify the precision of the estimations. We find that the quantum Fisher information with respect to the decoherence rate scales like $t^2/[\exp(γt)-1]$ and $\exp(-2γt)$ in the unitary limit and the completely decoherent limit, respectively. When we estimate the interaction strength $v$, the quantum Fisher information shows oscillation behavior in term of time. In addition, our results provide further evidence that the entanglement of the input state may not enhance quantum metrology.

arXiv:1401.2733Jan 13, 20140 citations

Quantum thermometry in a squeezed thermal bath

H Rangani Jahromi

Abstract We address the dephasing dynamics of the quantum Fisher information for the process of quantum thermometry with probes coupled to squeezed thermal baths via the nondemolition interaction. We also calculate the upper bound for the parameter estimation and investigate how the optimal estimation is affected by the initial conditions and decoherence, particularly the squeezing parameters. Moreover, the feasibility of the optimal measurement of the temperature is discussed in detail. Then, the results are generalized for entangled probes and the multi-qubit scenarios for probing the temperature are analysed. Our results show that the squeezing can decrease the number of channel uses for optimal thermometry. Comparing different schemes for multi-qubit estimation, we find that an increase in the number of the qubits, interacting with the channel, does not necessarily vary the precision of estimating the temperature. Besides, we discuss the enhancement of the quantum thermometry using the parallel strategy and starting from the W state.Abstract We address the dephasing dynamics of the quantum Fisher information for the process of quantum thermometry with probes coupled to squeezed thermal baths via the nondemolition interaction. We also calculate the upper bound for the parameter estimation and investigate how the optimal estimation is affected by the initial conditions and decoherence, particularly the squeezing parameters. Moreover, the feasibility of the optimal measurement of the temperature is discussed in detail. Then, the results are generalized for entangled probes and the multi-qubit scenarios for probing the temperature are analysed. Our results show that the squeezing can decrease the number of channel uses for optimal thermometry. Comparing different schemes for multi-qubit estimation, we find that an increase in the number of the qubits, interacting with the channel, does not necessarily vary the precision of estimating the temperature. Besides, we discuss the enhancement of the quantum thermometry using the parallel strategy and starting from the W state.

arXiv:1812.05968Physica ScriptaOct 15, 201914 citations

Quantum coherence of two-qubit over quantum channels with memory

You-neng Guo, Qinglong Tian, Ke Zeng +1 more

arXiv:1612.08791Quantum Information ProcessingNov 8, 201721 citations

Estimation of two-qubit interactions through channels with environment assistance

Milajiguli Rexiti, Stefano Mancini

We consider the estimation of two-qubit interactions when initial states of both qubit can be locally controlled, while the final state of only one qubit can be measured. This amounts to realize a model of quantum channel communication with environment assistance. In such a framework, the unitaries’ parameters space results a tetrahedron in [Formula: see text]. On its edges the problem, becoming of single parameter estimation, can be exactly solved and we derive optimal probe states and estimators. Our results show that the possibility of environment assistance is always beneficial, while the usage of entanglement at channels’ input is not.We consider the estimation of two-qubit interactions when initial states of both qubit can be locally controlled, while the final state of only one qubit can be measured. This amounts to realize a model of quantum channel communication with environment assistance. In such a framework, the unitaries’ parameters space results a tetrahedron in [Formula: see text]. On its edges the problem, becoming of single parameter estimation, can be exactly solved and we derive optimal probe states and estimators. Our results show that the possibility of environment assistance is always beneficial, while the usage of entanglement at channels’ input is not.

arXiv:1710.06248International Journal of Quantum InformationOct 1, 20174 citations

Optimal Estimation of Qubit States with Continuous Time Measurements

Mădălin Guţǎ, Bas Janssens, Jonas Kahn

arXiv:quant-ph/0608074Communications in Mathematical PhysicsOct 26, 200736 citations

γ

and the two-qubit interaction strength

v

. In particular, the dynamics of quantum Fisher information are employed as a measure to quantify the precision of the estimations. We find that the quantum Fisher information with respect to the decoherence rate scales like

t^2/[\exp(γt)-1]

and

\exp(-2γt)

in the unitary limit and the completely decoherent limit, respectively. When we estimate the interaction strength

v

, the quantum Fisher information shows oscillation behavior in term of time. In addition, our results provide further evidence that the entanglement of the input state may not enhance quantum metrology.