Final Report Summary - QUANTUM CONTROL (Tailoring decoherence for controlling spin systems: Deepening foundations; expanding applications)
During the last decades quantum control methods have developed into a central research subject in Physics. Improvements in the understanding of these quantum phenomena are enabling the use of these effects in a growing number of applications. In particular new control methods have been emerging for extending the life of quantum states and manipulating their targeted transfers, which can influence numerous areas of application ranging from spintronics to spin-based quantum computers and onto biological applications. This project expanded precisely this combination of basic principles and applications: starting from hitherto unexplored foundations of quantum control methods for tailoring spin evolutions, we gained a better understanding of these and tailored them into applications in the areas of nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) to be applied on macroscopic and nanoscale ensembles. The achievement of these dual goals, involved quantum-mechanical basic developments and spectroscopically-aimed applications for chemistry, biophysics and medicine, and were explored in the interdisciplinary environment that the Weizmann Institute of Science offered for these purposes.
The project focused on the use of quantum control processes based on tailoring decoherence processes for two specific purposes: (a) optimizing excitation/polarization transfer schemes, and (b) developing new spectroscopic methods based on the generation of controlled time-interference patterns for characterizing couplings and dynamics in complex chemical and physical systems, in anisotropic materials, and in tissues exhibiting restricted diffusion. In the following, we further define these problems and explain our results.
(a) Optimizing excitation/polarization transfer schemes
We developed a series of methods for transferring excitation/polarization from source spins to other group of spins. We exploited the use of relaxation processes as projective measurements combined with dynamical control strategies to make the polarization transfer robust and efficient when resonance condition cannot be attained [1]. Some methods were designed to polarize nuclear spins in solid-state powders where random orientations avoid achieving resonance conditions for all members of the powder. These results demonstrate with proof of principle solid-state experiments novel room-temperature hyperpolarization approaches for 13C nuclear spins in diamond with NV centers [2]-[4]. These principles may facilitate a number of applications. One entails facilitating the use of pre-polarized diamonds in NMR experiments, thanks to the ease with which NV electrons can be optically pumped by comparison with conventional cryogenic-based high-field counterparts. This easing of the hyperpolarization conditions should also facilitate the use of these samples in multi-scan acquisition, of the kind desirable in in-vivo MRI scans. Further technical implementations and optimizations of these methods on powders of diamonds need to be explored for the extension to applications of biological, chemical or medical interest. The fact that the method can polarize diamond powders is useful on these instances since nanodiamonds can be injected in materials (including biological samples) to be used for tracing purposes or to transfer the polarization to nuclei outside of the diamonds. We have also designed optimal modulation shapes of driving control fields for optimizing the transfer of polarization or excitations. This was done theoretically on simple models to find analytical results as a step towards understanding the main ingredients that need to be faced on complex systems as in proteins or quantum devices [5]. In particular we focused on optimizing the robustness of these approaches against typical experimental imperfections and heterogeneities of the system [5]-[7]. For this purpose, we experimentally addressed the limitations for transferring excitations in space in a controlled fashion in dipolar-coupled spin-systems (typical in NMR). We implemented condensed-matter tools to experimentally characterize the spreading of excitations and their limitations in a complex many-spin system with NMR experiments [8]-[9]. These results provide the conditions that need to be fulfilled in order to spread the excitations over a given system size in order to be able to process quantum information on complex and large quantum systems.
(b) Developing new spectroscopic methods based on the generation of controlled time-interference patterns
We developed spin-echo (dynamical decoupling) sequences based on our method termed Selective Dynamical Recoupling (SDR) [10] to selectively address specific information from the probed systems for NMR/MRI purposes. The methods were designed to use spins as quantum probes of their environment, whose dynamics can be characterized by generalized diffusion processes. We developed a theoretical framework for characterizing these processes where novel general fundamental concepts were found providing an alternative way for monitoring decoherence processes by generating coherent modulations [11]. Complementing these results with quantum information theoretical tools, we found a recipe to optimally measure a parameter that characterizes a physical, chemical or biological process by optimizing the tradeoff between the parametric sensitivity and the strength of the spin signal [12]. We developed different optimal approaches to determine efficiently different types of system parameters of interest in NMR and MRI scenarios. These methods are either useful on macroscopic ensembles as detected in conventional NMR, but also on few spins localized on nanoscales when optically detected NMR experiments are performed using NV centers [12]. We showed that for estimating parameters that quantify the environmental fluctuations, spin-echo sequences are optimal to estimate them in the lowest number of measurements. This is of particular interest for NMR/MRI in-vivo applications, where the total experimental acquisition times needs to be reduced for practical reasons to avoid movement’s distortions. Instead, if the coupling strength with the environment needs to be determined, we demonstrated that implementing the quantum Zeno effect induced by projective measurements is the most efficient and reliable estimation in this case. These results demonstrated by fundamental principles the optimal nature of previously developed methodologies by us for estimating spin-coupling network in NMR [13]. Based on these fundamental principles, we developed a series of SDR based methodologies for characterizing diffusion processes as novel tools for NMR and MRI spectroscopy [14]-[18]. These applications were based on estimating parameters like pore lengths in restricted diffusion, magnetic field gradients generated by pores structures, asymmetry parameters of geometrical shapes, coupling strengths, etc. One of our main results is the achievement of an unprecedented parametric sensitivity to restriction lengths of the diffusion processes that can attain nanometric resolution [11]. Applications of these new and simple approaches can be found in materials sciences and biology to extract the sizes of pores or cells in a non-invasive manner, in particular for investigating the nature of tissue compartmentalization [14]-[18], in manners which eventually could be useful in human and clinical settings.
[1]. G.A. Álvarez, D.D.B. Rao, L. Frydman, and G. Kurizki, Phys. Rev. Lett. 105, 160401 (2010).
[2]. G.A. Álvarez, C.O. Bretschneider, R. Fischer, P. London, H. Kanda, S. Onoda, J. Isoya, D. Gershoni, and L. Frydman. Submitted (2014). arXiv:1412.8635.
[3]. C.O. Bretschneider, G.A. Álvarez, R. Fischer, P. London, D. Gershoni, L. Frydman. “Can 13C in Diamond Powders be Polarized in Single-Digit Gauss Fields?”. 56th Experimental Nuclear Magnetic Resonance Conference (ENC), Asilomar Conference Center, Pacific Grove, California, USA (April 19-24, 2015). To be submitted for publication (2015).
[4]. C.O. Bretschneider, G.A. Alvarez, R. Fischer, P. London, D. Gershoni, L. Frydman. “Robust Level Anti-Crossing Induced 13C Hyper-polarization in 10% Enriched Diamond Crystals”. 56th Experimental Nuclear Magnetic Resonance Conference (ENC), Asilomar Conference Center, Pacific Grove, California, USA (April 19-24, 2015). To be submitted for publication (2015).
[5]. A. Zwick, G.A. Álvarez, G. Bensky, and G. Kurizki, New J. Phys. 16, 065021 (2014).
[6]. J. Stolze, G.A. Álvarez, O. Osenda, and A. Zwick in Quantum State Transfer and Network Engineering, edited by G. M. Nikolopoulos and I. Jex (Springer Berlin Heidelberg, 2014), pp. 149–182.
[7]. A. Zwick, G.A. Álvarez, J. Stolze, and O. Osenda, Quant. Inf. Comm. 15, 582 (2015).
[8]. G.A. Álvarez, R. Kaiser, and D. Suter, Ann. Phys. 525, 833 (2013).
[9]. G.A. Álvarez, Dieter Suter, and Robin Kaiser. Submitted (2014). arXiv:1409.4562.
[10]. P.E.S. Smith, G. Bensky, G.A. Álvarez, G. Kurizki, and L. Frydman, Proc. Natl. Acad. Sci. U. S. A. 109, 5958 (2012).
[11]. G.A. Álvarez, N. Shemesh, and L. Frydman, Phys. Rev. Lett. 111, 080404 (2013).
[12]. A. Zwick, G.A. Álvarez, and G. Kurizki. Maximizing information on the environment by controlled spin probes. Submitted (2014).
[13]. C.O. Bretschneider, G.A. Álvarez, G. Kurizki, and L. Frydman, Phys. Rev. Lett. 108, 140403 (2012).
[14]. N. Shemesh, G.A. Álvarez, and L. Frydman, J. Magn. Reson. 237, 49 (2013).
[15]. G.A. Álvarez, N. Shemesh, and L. Frydman, J. Chem. Phys. 140, 084205 (2014).
[16]. N. Shemesh, G.A. Álvarez, and L. Frydman. Size distribution imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI. To appear in PLOS ONE (2015).
[17]. N. Shemesh, G.A. Alvarez, and L. Frydman. To be submitted (2014). “Probing Internal-Gradient-Distribution-Tensors (IGDT) by Non-Uniform Oscillating-Gradient Spin-Echo (NOGSE) MRI: A New Approach to Map Orientations in Biological Tissues”. Joint Annual Meeting ISMRM-ESMRMB 2014, Milan, Italy (10-16 May 2014). To be submitted for publication (2015).
[18]. Critical behavior on the maximized information on the environment enlighten by dynamical control. A. Zwick, G.A. Álvarez, and G. Kurizki. To be submitted (2015).
The project focused on the use of quantum control processes based on tailoring decoherence processes for two specific purposes: (a) optimizing excitation/polarization transfer schemes, and (b) developing new spectroscopic methods based on the generation of controlled time-interference patterns for characterizing couplings and dynamics in complex chemical and physical systems, in anisotropic materials, and in tissues exhibiting restricted diffusion. In the following, we further define these problems and explain our results.
(a) Optimizing excitation/polarization transfer schemes
We developed a series of methods for transferring excitation/polarization from source spins to other group of spins. We exploited the use of relaxation processes as projective measurements combined with dynamical control strategies to make the polarization transfer robust and efficient when resonance condition cannot be attained [1]. Some methods were designed to polarize nuclear spins in solid-state powders where random orientations avoid achieving resonance conditions for all members of the powder. These results demonstrate with proof of principle solid-state experiments novel room-temperature hyperpolarization approaches for 13C nuclear spins in diamond with NV centers [2]-[4]. These principles may facilitate a number of applications. One entails facilitating the use of pre-polarized diamonds in NMR experiments, thanks to the ease with which NV electrons can be optically pumped by comparison with conventional cryogenic-based high-field counterparts. This easing of the hyperpolarization conditions should also facilitate the use of these samples in multi-scan acquisition, of the kind desirable in in-vivo MRI scans. Further technical implementations and optimizations of these methods on powders of diamonds need to be explored for the extension to applications of biological, chemical or medical interest. The fact that the method can polarize diamond powders is useful on these instances since nanodiamonds can be injected in materials (including biological samples) to be used for tracing purposes or to transfer the polarization to nuclei outside of the diamonds. We have also designed optimal modulation shapes of driving control fields for optimizing the transfer of polarization or excitations. This was done theoretically on simple models to find analytical results as a step towards understanding the main ingredients that need to be faced on complex systems as in proteins or quantum devices [5]. In particular we focused on optimizing the robustness of these approaches against typical experimental imperfections and heterogeneities of the system [5]-[7]. For this purpose, we experimentally addressed the limitations for transferring excitations in space in a controlled fashion in dipolar-coupled spin-systems (typical in NMR). We implemented condensed-matter tools to experimentally characterize the spreading of excitations and their limitations in a complex many-spin system with NMR experiments [8]-[9]. These results provide the conditions that need to be fulfilled in order to spread the excitations over a given system size in order to be able to process quantum information on complex and large quantum systems.
(b) Developing new spectroscopic methods based on the generation of controlled time-interference patterns
We developed spin-echo (dynamical decoupling) sequences based on our method termed Selective Dynamical Recoupling (SDR) [10] to selectively address specific information from the probed systems for NMR/MRI purposes. The methods were designed to use spins as quantum probes of their environment, whose dynamics can be characterized by generalized diffusion processes. We developed a theoretical framework for characterizing these processes where novel general fundamental concepts were found providing an alternative way for monitoring decoherence processes by generating coherent modulations [11]. Complementing these results with quantum information theoretical tools, we found a recipe to optimally measure a parameter that characterizes a physical, chemical or biological process by optimizing the tradeoff between the parametric sensitivity and the strength of the spin signal [12]. We developed different optimal approaches to determine efficiently different types of system parameters of interest in NMR and MRI scenarios. These methods are either useful on macroscopic ensembles as detected in conventional NMR, but also on few spins localized on nanoscales when optically detected NMR experiments are performed using NV centers [12]. We showed that for estimating parameters that quantify the environmental fluctuations, spin-echo sequences are optimal to estimate them in the lowest number of measurements. This is of particular interest for NMR/MRI in-vivo applications, where the total experimental acquisition times needs to be reduced for practical reasons to avoid movement’s distortions. Instead, if the coupling strength with the environment needs to be determined, we demonstrated that implementing the quantum Zeno effect induced by projective measurements is the most efficient and reliable estimation in this case. These results demonstrated by fundamental principles the optimal nature of previously developed methodologies by us for estimating spin-coupling network in NMR [13]. Based on these fundamental principles, we developed a series of SDR based methodologies for characterizing diffusion processes as novel tools for NMR and MRI spectroscopy [14]-[18]. These applications were based on estimating parameters like pore lengths in restricted diffusion, magnetic field gradients generated by pores structures, asymmetry parameters of geometrical shapes, coupling strengths, etc. One of our main results is the achievement of an unprecedented parametric sensitivity to restriction lengths of the diffusion processes that can attain nanometric resolution [11]. Applications of these new and simple approaches can be found in materials sciences and biology to extract the sizes of pores or cells in a non-invasive manner, in particular for investigating the nature of tissue compartmentalization [14]-[18], in manners which eventually could be useful in human and clinical settings.
[1]. G.A. Álvarez, D.D.B. Rao, L. Frydman, and G. Kurizki, Phys. Rev. Lett. 105, 160401 (2010).
[2]. G.A. Álvarez, C.O. Bretschneider, R. Fischer, P. London, H. Kanda, S. Onoda, J. Isoya, D. Gershoni, and L. Frydman. Submitted (2014). arXiv:1412.8635.
[3]. C.O. Bretschneider, G.A. Álvarez, R. Fischer, P. London, D. Gershoni, L. Frydman. “Can 13C in Diamond Powders be Polarized in Single-Digit Gauss Fields?”. 56th Experimental Nuclear Magnetic Resonance Conference (ENC), Asilomar Conference Center, Pacific Grove, California, USA (April 19-24, 2015). To be submitted for publication (2015).
[4]. C.O. Bretschneider, G.A. Alvarez, R. Fischer, P. London, D. Gershoni, L. Frydman. “Robust Level Anti-Crossing Induced 13C Hyper-polarization in 10% Enriched Diamond Crystals”. 56th Experimental Nuclear Magnetic Resonance Conference (ENC), Asilomar Conference Center, Pacific Grove, California, USA (April 19-24, 2015). To be submitted for publication (2015).
[5]. A. Zwick, G.A. Álvarez, G. Bensky, and G. Kurizki, New J. Phys. 16, 065021 (2014).
[6]. J. Stolze, G.A. Álvarez, O. Osenda, and A. Zwick in Quantum State Transfer and Network Engineering, edited by G. M. Nikolopoulos and I. Jex (Springer Berlin Heidelberg, 2014), pp. 149–182.
[7]. A. Zwick, G.A. Álvarez, J. Stolze, and O. Osenda, Quant. Inf. Comm. 15, 582 (2015).
[8]. G.A. Álvarez, R. Kaiser, and D. Suter, Ann. Phys. 525, 833 (2013).
[9]. G.A. Álvarez, Dieter Suter, and Robin Kaiser. Submitted (2014). arXiv:1409.4562.
[10]. P.E.S. Smith, G. Bensky, G.A. Álvarez, G. Kurizki, and L. Frydman, Proc. Natl. Acad. Sci. U. S. A. 109, 5958 (2012).
[11]. G.A. Álvarez, N. Shemesh, and L. Frydman, Phys. Rev. Lett. 111, 080404 (2013).
[12]. A. Zwick, G.A. Álvarez, and G. Kurizki. Maximizing information on the environment by controlled spin probes. Submitted (2014).
[13]. C.O. Bretschneider, G.A. Álvarez, G. Kurizki, and L. Frydman, Phys. Rev. Lett. 108, 140403 (2012).
[14]. N. Shemesh, G.A. Álvarez, and L. Frydman, J. Magn. Reson. 237, 49 (2013).
[15]. G.A. Álvarez, N. Shemesh, and L. Frydman, J. Chem. Phys. 140, 084205 (2014).
[16]. N. Shemesh, G.A. Álvarez, and L. Frydman. Size distribution imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI. To appear in PLOS ONE (2015).
[17]. N. Shemesh, G.A. Alvarez, and L. Frydman. To be submitted (2014). “Probing Internal-Gradient-Distribution-Tensors (IGDT) by Non-Uniform Oscillating-Gradient Spin-Echo (NOGSE) MRI: A New Approach to Map Orientations in Biological Tissues”. Joint Annual Meeting ISMRM-ESMRMB 2014, Milan, Italy (10-16 May 2014). To be submitted for publication (2015).
[18]. Critical behavior on the maximized information on the environment enlighten by dynamical control. A. Zwick, G.A. Álvarez, and G. Kurizki. To be submitted (2015).