Measurement of the Noise Spectrum Using a Multiple-Pulse Sequence

Abstract

A method is proposed for obtaining the spectrum for noise that causes the phase decoherence of a qubit directly from experimentally available data. The method is based on a simple relationship between the spectrum and the coherence time of the qubit in the presence of a π pulse sequence. The relationship is found to hold for every system of a qubit interacting with the classical-noise, bosonic, and spin baths.

Optimal control for non-Markovian open quantum systems

“…The presented QOCT has been shown to be a powerful tool, capable of facilitating implementations of various quantum information tasks against decoherence. The required information is knowledge of the bath or noise spectral density which is experimentally accessible by, for example, dynamical decoupling noise spectroscopy techniques [31][32][33][34][35]. We note here that not only our proposed method of QOCT but also dynamical decoupling and other strategies for fighting decoherence require knowledge of the spectral distribution of the noise (bath spectral density) in order to improve the strategies and design effective and/or optimized control sequences [12,13,[36][37][38][39].…”

“…We note here that not only our proposed method of QOCT but also dynamical decoupling and other strategies for fighting decoherence require knowledge of the spectral distribution of the noise (bath spectral density) in order to improve the strategies and design effective and/or optimized control sequences [12,13,[36][37][38][39]. Thus using the dynamical decoupling noise spectroscopy techniques [31][32][33][34][35] to determine the bath spectral densities experienced by the qubits and then applying QOCT to find explicitly control sequences for quantum gate operations for the non-Markovian open qubit system will yield fast quantum gates with low invested energy and high fidelity . By virtue of its generality and efficiency, our Krotov based QOCT method will find useful applications in many different branches of the sciences.…”

Sensitivity, quantum limits, and quantum enhancement of noise spectroscopies

“…Finally, we show sensitivity beyond the atom-and photon-number-optimized global standard quantum limit using squeezed light. , and quantum information processing [12][13][14][15][16]. By the fluctuation-dissipation theorem, the noise spectrum under thermal equilibrium gives the same information as do driven spectroscopies, with the advantage of characterizing the system in its natural, undisturbed state [17].…”

“…Conclusions -We have derived the sensitivity of noise spectroscopies from estimation theory, finding simple expressions for the Fisher information matrix in terms of the spectral model. The result enables rigorous use of noise spectra in cell biology [5,6], molecular biophysics [7,8], geophysics [9], space science [10], and quantum in- formation processing [12][13][14][15][16]. For optically-probed particulate systems that show line-broadening, e.g.…”

“…Noise spectroscopies, in which naturally occurring fluctuations of a system of interest are recorded by a noninvasive probe, have applications in a wide range of disciplines including atomic [1] and solid state physics [2,3], surface science [4], cell biology [5,6], molecular biophysics [7,8], geophysics [9], space science [10], quantum optomecanics [11], and quantum information processing [12][13][14][15][16]. By the fluctuation-dissipation theorem, the noise spectrum under thermal equilibrium gives the same information as do driven spectroscopies, with the advantage of characterizing the system in its natural, undisturbed state [17].…”