Aharonov’s weak value amplification realized via weak measurement provides a versatile means to measure physical parameters with high accuracy, similar to quantum resonance epitomized by the Rabi and Ramsey resonances. The similarity between the two is not accidental: in fact, these two methods of precision measurement have recently been shown to be interconnected for the particular case of direct weak measurement. Here we show that this connection also holds in the case of indirect weak measurement, which is the standard scheme used mostly for studies of weak value amplification. We present a unified framework of weak measurements in which direct measurement appears as a special case of indirect measurement. This allows us to compare the measurement precision of different methods on a common basis, as demonstrated explicitly for the Rabi and Ramsey resonances, showing how the precision of the latter surpasses that of the former in the context of weak value amplification.
Aharonov’s weak value amplification realized via weak measurement provides a versatile means to measure physical parameters with high accuracy, similar to quantum resonance epitomized by the Rabi and Ramsey resonances. The similarity between the two is not accidental: in fact, these two methods of precision measurement have recently been shown to be interconnected for the particular case of direct weak measurement. Here we show that this connection also holds in the case of indirect weak measurement, which is the standard scheme used mostly for studies of weak value amplification. We present a unified framework of weak measurements in which direct measurement appears as a special case of indirect measurement. This allows us to compare the measurement precision of different methods on a common basis, as demonstrated explicitly for the Rabi and Ramsey resonances, showing how the precision of the latter surpasses that of the former in the context of weak value amplification.
Abstract Quantum resonance, i.e., amplification in transition probability available under certain conditions, offers a powerful means for determining fundamental quantities in physics, including the time duration of the second adopted in the SI units and neutron’s electric dipole moment which is directly linked to CP violation. We revisit two of the typical examples, the Rabi resonance and the Ramsey resonance, and show that both of these represent the weak value amplification when involving significant enhancement of transition probabilities and that near the resonance points they share exactly the same behavior of transition probabilities except for the measurement strength whose difference leads to the known advantage of the Ramsey resonance in the sensitivity. Conversely, as a by-product of the relationship, we may measure the weak value through quantum resonance. In fact, we argue that previous measurements of neutron electric dipole moment based on the Ramsey resonance have potentially determined the weak value of neutron’s spin with much higher precision than the conventional weak value measurement.
The ability to manipulate light has allowed scientists to verify fundamental theories of physics and to develop a new generation of technologies that use photons as a primary resource. Recent developments in quantum measurement theory have offered new alternatives to approach some of the most remarkable problems in quantum physics. Consequently, the principles of quantum mechanics have been exploited in the development of quantum technologies such as optical metrology, quantum communication, and quantum information. In recent years, weak measurements and two of its most remarkable variants: weak value amplification and direct measurement, have been developed and are considered important resources for quantum applications. In this paper, we discuss weak measurements and some significant applications of weak values. We elaborate on how distinct forms of weak values are used to observe and amplify small effects or to directly measure the quantum wave function of photons, a crucial task for schemes for quantum communication and quantum information. We also review some of the most recent methods for weak value amplification and direct measurement that our group has developed.
The weak-value (WV) measurement proposed by Aharonov, Albert, and Vaidman (AAV) has attracted a great deal of interest in connection with quantum metrology. In this paper, we extend the analysis beyond the AAV limit and obtain a few main results. (i) We obtain a nonperturbative result for the signal-to-noise ratio (SNR). In contrast to the AAV prediction, we find that the SNR asymptotically gets worse when the AAV WV Aw becomes large, i.e., in the case $g|{A}_{w}{|}^{2}\ensuremath{\gg}1$, where g is the measurement strength. (ii) With the increase of g (but also small), we find that the SNR is comparable to the result under the AAV limit, while both can reach---actually the former can slightly exceed---the SNR of the standard measurement. However, with a further increase of g, the WV technique will become less efficient than the standard measurement, despite the fact that the postselection probability is increased. (iii) We find that the Fisher information can characterize the estimate precision qualitatively well as the SNR, yet the difference will become more prominent with the increase of g. (iv) We carry out analytic expressions of the SNR in the presence of technical noises and illustrate the particular advantage of the imaginary WV measurement. The nonperturbative result of the SNR manifests a favorable range of the noise strength and allows an optimal determination.
Abstract We present a general framework of examining the validity of weak measurement—the standard procedure to acquire Aharonov’s weak value—which has been used intensively in recent years for precision measurement, exploiting the amplification mechanism available for the weak value. Our framework allows one to deal systematically with various causes of uncertainties intrinsic to the actual measurement process as well as those found in the theoretical analysis employed to describe the system. Using our framework, we examine in detail the two seminal experiments, Hosten’s detection measurement of the spin Hall effect of light [Hosten and Kwiat 2008 Science 319 787] and Dixon’s ultra sensitive beam deflection measurement [Dixon et al 2009 Phys. Rev. Lett. 102 173601]. Our analysis shows that their results are well within the range of amplification (actually in the vicinity of the optimal point) where the weak measurements are valid. This suggests that our framework is both practical and sound, and may be useful to determine beforehand the possible extent of amplification in the future weak measurement experiments.
We present a general framework of examining the validity of weak measurement -- the standard procedure to acquire Aharonov's weak value -- which has been used intensively in recent years for precision measurement, taking advantage of the amplification mechanism available for the weak value. Our framework allows one to deal systematically with various causes of uncertainties intrinsic to the actual measurement process as well as those found in the theoretical analysis employed to describe the system. Using our framework, we examine in detail the two seminal experiments, Hosten's detection measurement of the spin Hall effect of light and Dixon's ultra sensitive beam deflection measurement. Our analysis shows that their results are well within the range of amplification (actually in the vicinity of the optimal point) where the weak measurements are valid. This suggests that our framework is both practical and sound, and may be useful to determine beforehand the possible extent of amplification in the future weak measurement experiments.
Weak measurement refers to a type of quantum measurement that disturbs the system very little. In the framework of weak measurement, Aharonov, Albert, and Vaidman introduced the concept of postselection and thereby defined the weak value. In recent research, weak-value measurement (WVM) has offered a novel perspective for studying intricate problems in quantum mechanics, leading to many conceptual breakthroughs. More importantly in practice, WVM has shown an unprecedented impact on precision sensing. In this review, we begin by presenting the fundamental theory of WVM based on quantum parameter estimation, from which the effects of weak-value amplification and weak-coupling amplification can be derived. The two effects can significantly improve the precision in various sensing schemes based on WVM. We point out the technical advantages that enable the WVM schemes to outperform the conventional ones under the same measurement conditions. Notably, the capability of information compression is underscored, which is garnering increasing attention in the field of quantum metrology. This review aims to show the possibility for broadening the application of WVM to address more critical problems, and on the other hand, for leveraging its advantages to accomplish tasks that are currently unattainable, such that WVM could play a more important role in the future of precision sensing.