scholarly journals Optimal frequency measurements with quantum probes

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Simon Schmitt ◽  
Tuvia Gefen ◽  
Daniel Louzon ◽  
Christian Osterkamp ◽  
Nicolas Staudenmaier ◽  
...  
Keyword(s):  
Frequency Estimation ◽  
Frequency Discrimination ◽  
Quantum Limit ◽  
Resonance Spectroscopy ◽  
Optimal Frequency ◽  
Frequency Sensitivity ◽  
Frequency Measurements ◽  
Estimation Problems ◽  
Quantum Strategies ◽  
Fourier Limit

AbstractPrecise frequency measurements are important in applications ranging from navigation and imaging to computation and communication. Here we outline the optimal quantum strategies for frequency discrimination and estimation in the context of quantum spectroscopy, and we compare the effectiveness of different readout strategies. Using a single NV center in diamond, we implement the optimal frequency discrimination protocol to discriminate two frequencies separated by 2 kHz with a single 44 μs measurement, a factor of ten below the Fourier limit. For frequency estimation, we achieve a frequency sensitivity of 1.6 µHz/Hz2 for a 1.7 µT amplitude signal, which is within a factor of 2 from the quantum limit. Our results are foundational for discrimination and estimation problems in nanoscale nuclear magnetic resonance spectroscopy.

scholarly journals Quantum metrology with full and fast quantum control

Quantum ◽  
2017 ◽  
Vol 1 ◽  
pp. 27 ◽  
Author(s):  
Pavel Sekatski ◽  
Michalis Skotiniotis ◽  
Janek Kołodyński ◽  
Wolfgang Dür
Keyword(s):  
Quantum Control ◽  
Frequency Estimation ◽  
Fixed Number ◽  
Constant Factor ◽  
Quantum Limit ◽  
Single Shot ◽  
Standard Quantum Limit ◽  
Parallel Scheme ◽  
Rank One ◽  
Fast Control

We establish general limits on how precise a parameter, e.g. frequency or the strength of a magnetic field, can be estimated with the aid of full and fast quantum control. We consider uncorrelated noisy evolutions of N qubits and show that fast control allows to fully restore the Heisenberg scaling (~1/N^2) for all rank-one Pauli noise except dephasing. For all other types of noise the asymptotic quantum enhancement is unavoidably limited to a constant-factor improvement over the standard quantum limit (~1/N) even when allowing for the full power of fast control. The latter holds both in the single-shot and infinitely-many repetitions scenarios. However, even in this case allowing for fast quantum control helps to increase the improvement factor. Furthermore, for frequency estimation with finite resource we show how a parallel scheme utilizing any fixed number of entangled qubits but no fast quantum control can be outperformed by a simple, easily implementable, sequential scheme which only requires entanglement between one sensing and one auxiliary qubit.

scholarly journals Reduced GABAergic inhibition and abnormal sensory symptoms in children with Tourette syndrome

2015 ◽  
Vol 114 (2) ◽  
pp. 808-817 ◽  
Author(s):  
Nicolaas A. J. Puts ◽  
Ashley D. Harris ◽  
Deana Crocetti ◽  
Carrie Nettles ◽  
Harvey S. Singer ◽  
...  
Keyword(s):  
Tourette Syndrome ◽  
Sensory Processing ◽  
Discrimination Performance ◽  
Frequency Discrimination ◽  
Resonance Spectroscopy ◽  
Gaba Concentration ◽  
Physiological Basis ◽  
Impaired Performance ◽  
Motor Tics

Tourette Syndrome (TS) is characterized by the presence of chronic tics. Individuals with TS often report difficulty with ignoring (habituating to) tactile sensations, and some patients perceive that this contributes to a “premonitory urge” to tic. While common, the physiological basis of impaired tactile processing in TS, and indeed tics themselves, remain poorly understood. It has been well established that GABAergic processing plays an important role in shaping the neurophysiological response to tactile stimulation. Furthermore, there are multiple lines of evidence suggesting that a deficit in GABAergic transmission may contribute to symptoms found in TS. In this study, GABA-edited magnetic resonance spectroscopy (MRS) was combined with a battery of vibrotactile tasks to investigate the role of GABA and atypical sensory processing in children with TS. Our results show reduced primary sensorimotor cortex (SM1) GABA concentration in children with TS compared with healthy control subjects (HC), as well as patterns of impaired performance on tactile detection and adaptation tasks, consistent with altered GABAergic function. Moreover, in children with TS SM1 GABA concentration correlated with motor tic severity, linking the core feature of TS directly to in vivo brain neurochemistry. There was an absence of the typical correlation between GABA and frequency discrimination performance in TS as was seen in HC. These data show that reduced GABA concentration in TS may contribute to both motor tics and sensory impairments in children with TS. Understanding the mechanisms of altered sensory processing in TS may provide a foundation for novel interventions to alleviate these symptoms.

Optimal frequency measurements with maximally correlated states

1996 ◽  
Vol 54 (6) ◽  
pp. R4649-R4652 ◽  
Author(s):  
J. J . Bollinger ◽  
Wayne M. Itano ◽  
D. J. Wineland ◽  
D. J. Heinzen
Keyword(s):  
Optimal Frequency ◽  
Frequency Measurements

scholarly journals Restoring Heisenberg scaling in noisy quantum metrology by monitoring the environment

Quantum ◽  
2018 ◽  
Vol 2 ◽  
pp. 110 ◽  
Author(s):  
Francesco Albarelli ◽  
Matteo A. C. Rossi ◽  
Dario Tamascelli ◽  
Marco G. Genoni
Keyword(s):  
Detection Efficiency ◽  
Frequency Estimation ◽  
Quantum Fisher Information ◽  
Quantum Limit ◽  
Convexity Property ◽  
Quantum Metrology ◽  
Standard Quantum ◽  
Standard Quantum Limit ◽  
Photo Detection ◽  
Continuous Estimation

We study quantum frequency estimation for N qubits subjected to independent Markovian noise, via strategies based on time-continuous monitoring of the environment. Both physical intuition and an extended convexity property of the quantum Fisher information (QFI) suggest that these strategies are more effective than the standard ones based on the measurement of the unconditional state after the noisy evolution. Here we focus on initial GHZ states and on parallel or transverse noise. For parallel noise, i.e. dephasing, we show that perfectly efficient time-continuous photo-detection allows to recover the unitary (noiseless) QFI, and thus to obtain a Heisenberg scaling for every value of the monitoring time. For finite detection efficiency, one falls back to the noisy standard quantum limit scaling, but with a constant enhancement due to an effective reduced dephasing. Also in the transverse noise case we obtain that the Heisenberg scaling is recovered for perfectly efficient detectors, and we find that both homodyne and photo-detection based strategies are optimal. For finite detectors efficiency, our numerical simulations show that, as expected, an enhancement can be observed, but we cannot give any conclusive statement regarding the scaling. We finally describe in detail the stable and compact numerical algorithm that we have developed in order to evaluate the precision of such time-continuous estimation strategies, and that may find application in other quantum metrology schemes.

Spectroscopic imaging of human disease

1996 ◽  
Vol 54 ◽  
pp. 884-885
Author(s):  
D.J. Meyerhoff
Keyword(s):  
Magnetic Field ◽  
Magnetic Resonance ◽  
Field Gradient ◽  
Human Disease ◽  
Morphological Changes ◽  
Magnetic Field Gradient ◽  
Spectroscopic Imaging ◽  
Resonance Spectroscopy ◽  
Tissue Water

Magnetic Resonance Imaging (MRI) observes tissue water in the presence of a magnetic field gradient to study morphological changes such as tissue volume loss and signal hyperintensities in human disease. These changes are mostly non-specific and do not appear to be correlated with the range of severity of a certain disease. In contrast, Magnetic Resonance Spectroscopy (MRS), which measures many different chemicals and tissue metabolites in the millimolar concentration range in the absence of a magnetic field gradient, has been shown to reveal characteristic metabolite patterns which are often correlated with the severity of a disease. In-vivo MRS studies are performed on widely available MRI scanners without any “sample preparation” or invasive procedures and are therefore widely used in clinical research. Hydrogen (H) MRS and MR Spectroscopic Imaging (MRSI, conceptionally a combination of MRI and MRS) measure N-acetylaspartate (a putative marker of neurons), creatine-containing metabolites (involved in energy processes in the cell), choline-containing metabolites (involved in membrane metabolism and, possibly, inflammatory processes),

Frequency Discrimination in Regions of Normal and Impaired Sensitivity

1982 ◽  
Vol 25 (1) ◽  
pp. 34-41 ◽  
Author(s):  
Christopher W. Turner ◽  
David A. Nelson
Keyword(s):  
Frequency Discrimination
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