Monday, 10 July 2023
Quantum information science has changed our view of quantum mechanics. Originally viewed as a nag, whose uncertainty principles restrict what we can do, quantum mechanics is now seen as a liberator, allowing us to do things, such as secure key distribution and efficient computations, that could not be done in the realistic world of classical physics. Yet there is one area, that of quantum limits on high-precision measurements, where the two faces of quantum mechanics remain locked in battle. I will trace the history of quantum-limited measurements, from the use of nonclassical light to improve the phase sensitivity of an interferometer to the modern perspective on the role of entanglement in improving measurement precision.
In this lecture the need for an International System of Units (SI) will be outlined followed by the historical evolution of the SI with the Metre Convention. The latest definition of the length unit with the final one based on a fundamental constant, the speed of light, served as the blueprint of the latest revision of the SI where all base units are traced back to constants – fundamental ones and ones that keep the SI as a coherent system.
The main part of the lecture gives examples for quantum-metrology based standards for time and frequency, mass and the electric standards.
Finally, the future of the SI will be discussed where most likely optical atomic clocks will replace the current definition of the SI second based on the Cs hyperfine transition.
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I will introduce the basics of quantum metrology, including a discussion on essential elements of classical estimation theory, quantum states, phase acquisition, quantum measurements, local vs. global metrology and other topics.
The first part of this lecture deals with examples underpinning the need to express the estimated uncertainty of the result of any measurement that assures an overall quality management in science, industry, and medicine. General definitions are recalled together with the basics of the calculations of uncertainties.
In the second part the expression and reporting of uncertainties is treated as it is agreed upon worldwide in the Guide to the expression of uncertainty in measurement (GUM) with several examples.
Finally, the application of Monte Carlo methods as a means to determine uncertainties will be discussed.
Tuesday, 11 July 2023
This talk is a deep dive into why Fisher information and quantum Cramer-Rao bounds are the right way to place quantum limits of high-precision measurements.
This lecture exemplifies what has been derived in the lecture "Analysis of Uncertainties - I" by a Case Study: Evaluation of Uncertainty in an optical atomic clock.
The second part of the lecture deals with tips and tricks to reduce errors and uncertainties in measurements.
The lecture ends with examples on overlooked uncertainties and errors in important experiments.
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I will introduce the basics of quantum metrology, including a discussion on essential elements of classical estimation theory, quantum states, phase acquisition, quantum measurements, local vs. global metrology and other topics.
Even though we expect beyond-Standard-Model effects to operate at energy scales far beyond 10 TeV, remarkably, it is possible to measure their influence on atoms and molecules in low-energy precision experiments. In this series of three opinionated lectures, I will discuss /why/ it is possible to measure these effects, /how/ we have tried to measure them, and /what/ the future holds.
Wednesday, 12 July 2023
Even though we expect beyond-Standard-Model effects to operate at energy scales far beyond 10 TeV, remarkably, it is possible to measure their influence on atoms and molecules in low-energy precision experiments. In this series of three opinionated lectures, I will discuss /why/ it is possible to measure these effects, /how/ we have tried to measure them, and /what/ the future holds.
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Modern atomic clocks are known as the most precise instruments developed in the world till date. Apart from the time keeping devices, they are suitable for probing variation of the fine-structure constant, detection of dark matter, predicting volcanology and earthquake eruption etc.. It is imperative to use clocks with ultra-high precision (which can loose only one second over the age of our universe or less) for such predictions. Some of the clocks have already achieved similar accuracy, however further improvements over the accuracy of these clocks are desired for unambiguity interpretation of the findings. Again, searching for new clock candidates that can be least affected by external perturbations would be necessary to carry out the above probes than pushing hard with the existing clocks to improve their accuracy. In this context, I shall discuss about the roles of atomic many-body methods to support the atomic clock experiments as well as similar high-precision experiments carried out using table top facilities.
A pot pouri of (classical) methods used in laser interferometer gravitational-wave detectors to surpass the Standard Quantum Limit and some discussion of how to reach towards the nibbano of Heisenberg scaling.
Thursday, 13 July 2023
The laws of quantum mechanics determine the fundamental limits on the precision in a measurement and their dependence on the available resources. Techniques from quantum information theory can be used to make the relationship between the limits and resources transparent. In the prototypical quantum metrology scheme, the value of a parameter associated with a measured system is imprinted on a quantum probe made of n subunits through an interaction in which it appears as a coupling constant. The number of subunits in the probe is considered to be the most important resource in such measurement schemes. I discuss how well-studied quantum metrology schemes in which the interaction acts independently on the subunits of the probe can be translated into the language of quantum circuits. This lets us see the conditions under which the shot-noise limited scaling of 1/\sqrt{n} and the Heisenberg-limited scaling of 1/n for the measurement uncertainty may be achieved. We also see that if the interaction involves k-body couplings between the subunits then the measurement uncertainty can scale as 1/n^k, provided the probe is initialized in an entangled state, and as 1/n^{k-1/2}, if the probe is initially in a product state. With just two body couplings and no entanglement in the initial state of the probe it is possible to attain a scaling of 1/n^{3/2} and thereby improve upon the 1/n scaling that was previously thought to be the best that any quantum metrology scheme could do. The 1/n^{3/2} scaling can be achieved using both entangling and non-entangling Hamiltonians. It is the dynamics that leads to an improvement over the $1/n$ scaling. I show how such a metrology protocol may be implemented using a two mode Bose-Einstein condensate of Rb atoms. I also discuss the effect of decoherence on these metrology schemes.
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I shall cover working principle of the clock, advantages of atomic clocks, microwave clock, cesium fountains.
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Problem-solving and discussion attached to the previous two lectures.
Friday, 14 July 2023
I will review the state of the art of optical atomic clocks and today's performance of laboratory and portable systems.
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In this lecture, we will discuss few basic types of atomic magnetometry and compare the performances based on standard metrics of sensitivity, dynamic range and response times. We will end the lecture with a discussion of possible usage of atomic quantum memories for magnetic field sensing.
Monday, 17 July 2023
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Paul and Penning traps are exquisite tools to trap charged particles, store them for very long times, and interrogate them by electromagnetic fields. They allow to trap samples ranging from an individual particle to a large ion cloud, and have therefore found applications in a wide range of domains, from quantum information to non-neutral plasma physics. My lectures will focus on precision spectroscopy in traps of different charged particles (ions, electrons, antimatter, ..). I will review operation, performances, experimental conditions, and limits, and discuss some of today’s forefront experiments.
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An assay of noise estimation and modeling methods for precision experiments. Control system modeling, Bayesian inference, nullstreams, nonlinear noise regression.
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Tuesday, 18 July 2023
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Paul and Penning traps are exquisite tools to trap charged particles, store them for very long times, and interrogate them by electromagnetic fields. They allow to trap samples ranging from an individual particle to a large ion cloud, and have therefore found applications in a wide range of domains, from quantum information to non-neutral plasma physics. My lectures will focus on precision spectroscopy in traps of different charged particles (ions, electrons, antimatter, ..). I will review operation, performances, experimental conditions, and limits, and discuss some of today’s forefront experiments.
I will review modern applications of atomic clocks in relativistic geodesy and search for new physics.
Precision Measurement, Metrology, and Trade
A.K. Raychaudhuri#
SERB Distinguished Fellow
CSIR-Central Glass and Ceramic Research Institute, Kolkata
# Former Director, CSIR-National Physical Laboratory, New Delhi
Precision measurements form the back bone of metrology and physical standards. Important discoveries in Physics have enriched the field of Metrology and how the basic units of weights and measures be defined and physically realized. The unprecedented growth in the tools of precision measurements have given rise to new methods of metrology and definition of basic SI units. As a very recent example one can quote the definition of 1Kg where it is defined through Planck’ s constant. This is part of the current trend in metrology where it moves from artifact based definition to definitions based on Quantum Physics and Physical constants like h,e,c and k_B.
While physical realization of basic SI units is a domain of precision measurements, the units be disseminated to market place and shop floors to have merchandise and products conforming to certain stated standards. This forms the backbone of trade and commerce , an activity that was practised in ancient civilizations like Harappan and Egyptian civilizations. Now a days there are definite norms and methods that need be followed.
This talk will first make a case that the modern trade and commerce cannot flourish without a strong activity on precision measurements and metrology followed by Laboratory accreditation programme.
This will be followed by certain historical perspectives of development of modern metrology and SI units and its realization
Wednesday, 19 July 2023
Diamond serves as an ideal crystalline host for a variety of point defects due to its qualities such as wide band gap, small spin-orbit coupling and its availability in high quality, isotopically purified single crystals. Among the possible defects, the nitrogen-vacancy (NV) spin defect has been extensively studied as its spin state can be optically initialized and measured at room temperature, and can be manipulated via electron spin resonance by microwave radiation.
The NV center in diamond has been used to measure a number of physical quantities such as magnetic field, electric field, temperature and stress/strain at ambient conditions [1, 2]. Recent studies have shown that it can also be used as an atomic-scale probe of the charge and strain environments intrinsic to the diamond lattice [3,4]. In this talk, I'll discuss our high-resolution microwave spectroscopy studies using single NV centers in diamond.
References
1. R. Schirhagl et al, Annual Reviews in Physical Chemistry, 2014, 65, 83.
2. P. Peddibhotla et al, Nano Letters, 2017, 17 (3), 1496.
3. T. Mittiga et al, Phys. Rev. Lett. 121, 246402 (2018).
4. Shashank Kumar et al, 2023 Quantum Sci. Technol. 8 025011.
In this talk, we discuss the optical properties of quantum emitters like NV centers and devise methods that can enhance their utility in various applications ranging from tailored emission, quantum sensing, and bio-imaging. We have photonic cavities to control the spontaneous emission from the NV centers. The light transport properties of these structures are analyzed which shows the suppressed and enhanced photon density of states at the respective resonant modes. The modified emission properties of NV centers in frequency and time scale would be elaborated. The indigenous developments of a confocal microscope to map the isolated single NV centers and their emission characteristics would be discussed. I conclude the talk by discussing a few nanophotonics structure designs that can deterministically tune NV center emission properties.
CSIR-NPL is the National Measurement Institute (NMI) of India and mandated for realization and dissemination of the local Universal Coordinated Time, i.e., UTC(NPLI), and Indian Standard Time (IST). Current SI definition of time is defined as time required for 9192631770 cycles between two hyperfine energy levels of ground states of 133Cs atom separated by ~ 9.2 GHz. Atomic clocks with operational frequency in the optical domain, commonly known as optical clocks, are capable of providing ~ 1000 times better accuracy as well as stability than the microwave clocks and its expected that in near future the SI second will be redefined through optical clock. Neutral atoms e.g., 199Hg, 171Yb, 87Sr and 40Ca or atomic ions, e.g., 199Hg+, 171Yb+, 88Sr+, 43Ca+ and 27Al+ can provide better long term stability with a fractional frequency uncertainty ~ 10-18. Keeping in mind the possible redefinition of the SI second in the near future, CSIR-NPL has started developing an optical frequency standard based on the forbidden quadrupole transition at the wavelength ~ 435 nm of Ytterbium-ion (171Yb+). Ytterbium-ion is one of the prospective candidates for redefinition of the next generation SI second based on an optical transition and at present, it is defined as a secondary standard by the General Conference on Weights and Measures (CIPM). In this talk I will present our current activities related to time and frequency metrology including status of the optical clock development at CSIR-NPL.
Ensembles of nuclear spin networks in the bulk matter at ambient temperature retain quantum coherence for long durations while allowing intricate quantum control via nuclear magnetic resonance (NMR) techniques. We look at different aspects of precision measurements in such systems. In particular, we describe two approaches to improve precision: (i) space approach: using correlated states of a many-spin system, and (ii) time approach: extending the lifetime of quantum coherence. As examples, we describe an efficient measurement of translational diffusion constants in liquids, characterization of radio-frequency (RF) fields, extracting noise spectrum of multi-qubit systems, and ancilla-induced amplification of quantum Fisher information. Finally, we describe recent experiments on achieving precision measurements via weak-value amplification.
An optical cavity sustains discreet oscillations of an electromagnetic (EM) field, as determined by the boundary conditions of the cavity. Under usual operating conditions the confined EM field corresponds to a single mode of light. Atoms and molecules interact with EM fields by the response of bound electrons to the field. When atoms and molecules are placed in an optical cavity, their interaction with the cavity mode field changes the spectral response of the combined atom(molecule)-cavity system. This results in the possibility for the sensitive detection and probing of atoms/molecules using cavities. Here we discuss several aspects and experiments with the atom(molecule)-cavity system, emphasising on the detection of atoms and molecules using optical cavities.
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Thursday, 20 July 2023
Quantum annealing is one of the two paradigms of quantum computing. In my talk, I shall present our results of fine structure splittings (FSS) for boron-like ions based on the Quantum Annealer Eigenvalue (QAE) algorithm using the D-wave quantum hardware. Our results agree with high precision laboratory measurements of FSS in boron-like measurements to 99%. We achieved this high accuracy by rigorously including relativistic and many-body effects in the FSS computations in the framework of QAE and making improvements in the quantum annealing workflow.
With the advancement in cooling, trapping and manipulation techniques for neutral atoms, the use of cold atoms in various precision measurements is becoming a reality. There are many examples where use of cold atoms has shown accuracy in measurements comparable or better than that by state of art existing devices. These include measurement of time, magnetic field, acceleration, rotation, etc. In this talk, an overview of these advances will be presented. The recent developments at our laboratory related to precision measurements using cold atoms will also be discussed.
Precision measurements using atoms, ions, and molecules play a crucial role in fundamental physics studies, confirming theoretical predictions, and developing advanced technologies such as optical atomic clocks. Next-generation quantum devices rely on various technologies and physics principles, including AC Stark shifts, the magnetic Zeeman effect, and laser cooling. With these knowledge, I will discuss one specific example of precision measurement, i.e., the magic frequency of the 138Ba+ clock transition S1/2 -D5/2 state using a single ion. The choice of this transition and the experimental implementation of essential laser systems for achieving highly accurate magic frequency, which minimize systematic effects that could introduce uncertainties in the measurement will discuss. Our experimental technique have successfully provided measurements of the magic frequency with a precision that exceeds the previously predicted theoretical value by a factor of 103. This improvement offers an exciting opportunity for theoreticians to conduct more thorough studies and refine theoretical models to better understand the underlying physics of the system. By achieving such precise measurements, scientists can further validate theoretical predictions, explore fundamental physics, and enhance the development of advanced technologies that rely on the precise control and manipulation of atomic and ionic systems.
Atomic systems offer a plethora of fundamental and functional properties and, therefore, are of great importance to several implications. To mention some key phenomena where atoms are used as a probe includes atomic clocks [1], parity- and time-reversal violations [2,3], and the variation in the fundamental constants [4]. Atomic systems, however, form a complex many-body system for which getting exact solution is nontrivial. This poses a challenge in the theoretical investigations of the properties of these systems. In this context, relativistic coupled-cluster (RCC) theory is one of the most reliable many-body theories for atoms and ions.
In our group at IIT Delhi, we have developed a series of RCC based methods for the properties calculations of atomic systems. These methods are implemented as sophisticated parallel FORTRAN programs [5,6,7]. In this talk, I shall, after briefly discussing the RCC for two-valence, share some key clock properties results for group-13 elements [6,7] and Sr atomic clock [8].
References:
[1] Andrew D. Ludlow et. al., Rev. Mod. Phys. 87, 637 (2015).
[2] C. S. Wood et al., Science, 275, 1759 (1997).
[3] W. C. Griffith, et al., Phys. Rev. Lett. 102, 101601 (2009).
[4] S. G. Karshenboim and E. Peik, Lecture Notes in Physics (Springer, New York, 2010).
[5] B. K. Mani et. al., Comp. Phys. Comm. 213, 136 (2017).
[6] Ravi Kumar et. al., Phys. Rev. A. 103, 022801 (2021).
[7] Ravi Kumar et. al., Phys. Rev. A. 06, 032801 (2022).
[8] Palki et. al., (to be submitted)
Precision measurement of time, and its synchronisation, improved by a whopping factor 10^12 (trillion) during the past century. This was enabled by the development of atomic frequency standards and clocks, optical fiber technology, and global cooperation. After a brief survey of some milestones, I will explore the implications of precision metrology of time in fundamental physics. The interplay between time and gravity will be sketched in the context of motional time dilation and gravitational time dilation. I will explain the role of consensus and convention in a consistent global synchronisation of time, and then bring out a serious deficiency that demands a disruptive revision in the treatment of time in physics. Implications for satellite based positioning and navigational systems will be highlighted. I will conclude with some remarks about precision time and causality in quantum dynamics.
Friday, 21 July 2023
Spin associated with quantum defects such as Nitrogen-vacancy centres in diamond are the leading edge for nanoscale magnetic sensing. I will introduce relaxometry, i.e. using changes to spin-lattice relaxation for magnetic sensing and how it can be used with quantum sensors for performing nanoscale spectroscopy and imaging. Relaxometry can also enable the use of magnetic fields non-collinear with the NV axis. I will discuss the behavior of NV centers in such “off-axis” fields.
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Optical clocks represent the pinnacle of precise timekeeping. Precision optical atomic clocks provide the highest level of sensitivity are based on transitions in the optical domain using neutral atoms or trapped atomic ions and define international timescales, provide a basis for testing the time invariance of fundamental constants and lead to the search for new physics beyond the Standard Model. The other domain is the regime of portable atomic clocks based on warm atomic vapor, that are compact, low power consuming and are field deployable with a multitude of targeted applications in telecommunications, navigation (GPS), sensing and precision timing. With the increasing use of field-deployable atomic clocks and frequency standards, many commercial and strategic applications including sensing, communications and navigation, are getting a tremendous technological boost. It is imperative to develop technologies to enable the development of next-generation portable atomic clocks utilising optical transitions in trapped cooled ions/atoms for future applications.
At IIT Tirupati, we are engaged in developing the next generation all-optical trapped ion based portable frequency standards using optical transition in 40Ca+ (Calcium ion) for quantum positioning, quantum sensing and precision timing applications. We are working towards development of compact laser sources, electronics, and miniaturized vacuum systems for the all-optical trapped ion-based frequency standard. We shall present a brief overview of our research activities at IIT Tirupati in this domain and discuss some of the challenges and opportunities related to a host of quantum technology applications and search for New Physics (NP) beyond the Standard Model (SM).
Recently, our group demonstrated a phenomenon called magnetoelectric effect in thermal atomic vapor. Magnetoelectric effect is associated with the nonlinear optical processes where the mixing of RF-magnetic field and optical electric field lead to the generation of new optical fields. The detection of the newly generated optical fields due to these processes is the basis of detection of rf-magnetic field present in a medium of atomic vapor. We exploit the magnetoelectric effect for the application of precision rf-magnetometry. I will present the recent development of this program at NISER Bhubaneswar.
Neutral atoms in itself are very good sensors for magnetic fields, to measure coherence and making long lived atomic spin states, and laser cooled cold atoms - owing to the absence of thermal fluctuations and the opportunity to measure over a long time - offer excellent opportunities to be used in the context of quantum sensing and metrology.
In this talk, I shall discuss about the performance of a new experimental facility to simultaneously cool and trap neutral Sodium and Potassium atoms in large numbers. Thereafter, I shall present how we investigate interspecies interactions between these co-trapped cold atom clouds and the planned experiments in this system to study quantum many-body system with tunable interspecies interactions.
I shall show the “structured” optical tweezers as well as generation of orbital angular momentum states of light for exploring truly exotic atom-light interactions. The underlying ideas are in studying spin-fluctuations in coherently driven cold atoms with two photon excitations – a technique developed in our laboratory over the recent past. I shall describe the technique itself and results and applications in magnetometry and quantum sensing. Lab website: https://wwws.rri.res.in/~qumix
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Rydberg atoms are giant superatoms with the outer electron in a highly excited state with large values of the principal quantum number n. Rydberg atoms are highly sensitive to external fields imparting these atoms extraordinary characteristics for Precision Quantum sensing of electromagnetic fields.
I will present our recent experimental observations on Quantum sensing via Enhanced sensitivity of magnetometry using Quantum Interference in Rydberg atoms. I will also present our measurements on Rydberg excitation dynamics in cold atoms towards the investigation of the Quantum criticality of Rydberg atoms in lower dimensions arising due to strong dipole-dipole interactions.
In this presentation, we will present the results obtained by investigating the electromagnetic induced resonances in Rb-87 vapor on application of external magnetic fields. In presence of high magnetic field, the effect of close lying states become significant and its effects are observed in the lineshape of electromagnetic induced transparency(EIT). We observed asymmetric features which is attributed to the impurities in the dark states because of the presence of close lying states. This asymmetry in the line shape can be controlled by tuning the parameters like laser power, magnetic field and by using anti relaxation coating(ARC) vapor cell. We have demonstrated that by tuning external parameters, we can limit the interaction of various velocity classes responsible for asymmetry. We established our result by performing the experiments in ARC coated cell, where by limiting the velocity dependent population distribution we can overcome the asymmetry. Finally, we also investigated the effect of third laser on EIT. The third laser converts a bi-chromatic A type system into a four-level N-type system. Experimental studies reveal a switch from absorption to transmission depending on the detuning. This conversion is explained by light shift modification induced by the third laser. These presentation will present through understanding and optimization of EIT phenomena in 87Rb which have promising applications in optical switching and quantum magnetometry, contributing to the advancement of technologies in these fields.
Doppler-free two-photon spectroscopy is a standard technique for precision measurement of transition frequencies of dipole forbidden transitions, e.g. the s-s and s-d transitions in atoms. The accuracy of such measurements depends critically on accurate fitting of the spectrum to a model lineshape and on proper estimation of systematic effects. We observe, for the first time, a subtle systematic effect arising from quantum interference of optical transitions in two-photon spectroscopy. Quantum interference between optical transitions arises when there are two or more allowed optical pathways that connect an initial quantum state i to a final quantum state f. For example, consider the transitions i -> m -> f and i -> n -> f, which proceed via different intermediate states m and n. Quantum interference between the two pathways leads subtle but measurable effects in the line shape and line position of the optical transition. We find that the line shift is several 10 kHz in the case of the cesium 6s - 7d transition. We calculate the line shape including the effect of quantum interference and show that it resolves the apparent line shift. The results have implications for the measurement of hydrogen 1s-2s and 1s-3s transition frequencies, isotope shifts and hyperfine splittings.
As the national metrology institute (NMI) of India, CSIR-NPL sets, and disseminates the national standards for the seven SI units and the derived units. The redefinitions of the SI units in terms of the fundamental constants led to the rise of quantum metrology. As NMI, NPL is working on the quantum standards. In this talk I will present the current status and challenges of quantum metrology.