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TechConnect Briefs

Quantum Information Processing with Nuclear Spin-Based Devices

Paola Cappellaro, David G. Cory, Timothy F. Havel, Chandrasekhar Ramanathan

Published May 8, 2005• 0 citations
OpenAlex

Abstract

This talk will illustrate the benefits offered by QIP with two devices which use quantum entanglement among nuclear spins to perform high-precision measurements: (1) a spin gyroscope that operates by detecting the frequency shift in the spins precession rate in the rotating frame, which is potentially more accurate than mechanical or optical devices; (2) a quantum amplifier which correlates the states of a macroscopic number of nuclear spins with the state of a single target spin, so that a collective measurement of the state of the amplifier’s spins reveals that of the target spin. Some potential implementations of these devices based on nuclear spins in naturally occurring materials will also be described.

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We propose to implement a solid-state rotation sensor by employing a many-body quantum spin system which takes the advantages of the easy controllability of the electron spin and the robustness provided by the collective nuclear spin state. The sensor consists of a central electron spin coupled to many surrounding nuclear spins. Previously, this central spin system has been suggested to realize a quantum memory. Here, we further utilize the collective nuclear spins, which store a certain quantum state, to detect the macroscopic rotation. Different from other nuclear spin-based gyroscopes, our proposal does not directly manipulate nuclear spins via nuclear magnetic resonance technique. We analytically and numerically investigate the effects of partial nuclear polarization and decoherence on the sensitivity. We also briefly introduce the procedure to generate entanglement between nuclear spins through the quantum memory technique and to utilize this entanglement to enhance the sensing performance. Our proposal paves the way to the experimental realization of a compact solid-state, full-electrical, and spin-based gyroscope.

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Quantum computers are machines that exploit the quantum mechanical properties of physical systems to realize an exponential speed-up in problem-solving capability compared with existing computers. Existing schemes for the realization of such machines occur in diverse areas such as atomic physics, nuclear magnetic resonance, superconductivity, quantum optics and solid state physics. We are concerned here with the experimental realization of various elements needed for quantum information processing using nuclear spin immersed in a confined electronic system in the quantum Hall regime. Some distinguishing characteristics of this approach include the application of the Overhauser effect for dynamic nuclear polarization at relatively high temperatures, spin measurement using relatively simple electrical detection techniques, spin control with microwave/radio frequency methods, the utilization of the electronic spin exciton as a possible mobile spin transfer mechanism for the eventual realization of a logic gate, and the application of semiconductor technology to device integration. Concepts involved in this approach are also illustrated with experimental results.

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Coherent control of nuclear and electron spins for quantum information processing

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The ability to perform quantum error correction (QEC) arbitrarily many cycles is a significant challenge for scalable quantum information processing (QIP). Key requirements for multiple-round QEC are a high degree of quantum control, the ability to efficiently characterize both intrinsic and extrinsic noise, and the ability to dynamically and efficiently extract entropy from ancilla qubits. Nuclear Magnetic Resonance (NMR) based quantum devices have demonstrated high control fidelity with up to 12 qubits, and the noise characterizations can be performed using an efficient protocol known as randomized benchmarking. One of the remaining challenges with NMR systems is that qubit initialization is normally only attainable via thermal equilibration. This results in very low polarizations in reasonable experimental conditions. Moving to electron-nuclear coupled spin systems in a single crystal is a promising solution to the ancilla qubit preparation problem. One obvious advantage of incorporating electron spins comes from higher gyromagnetic ratio of the electron which yields about three orders of magnitude larger thermal spin polarization than that of nuclear spins in the same experimental condition. In addition, fast control of nuclear spins is possible provided appropriate level of anisotropic hyperfine interaction strength. The nuclear spins can be polarized even beyond the thermal electron spin temperature using a technique Heat-Bath Algorithmic Cooling (HBAC). With theoretical ideas in hand, the next step is to develop classical instrumentations to control electron-nuclear coupled systems and accomplish high fidelity coherent control. Noise characterizations are also necessary for benchmarking the quality of control over the electron-nuclear spin system. \nI first present example applications of NMR QIP with small number of qubits: Testing a foundational question in quantum mechanics and measuring spectral density of noise in a quantum system. Then I report on our home-built X-band electron spin resonance (ESR) spectrometer and progress in achieving high fidelity coherent control of electron and nuclear spins for QIP. We focus on implementing nuclear spin manipulation via anisotropic hyperfine interaction and microwave (mw) control, but discussions also include electron nuclear double resonance (ENDOR) control techniques. We perform realistic algorithmic simulations to show that an experimental cooling of nuclear spins below electron thermal temperature is feasible, and to present the electron-nuclear spin systems as promising testbeds for scalable QIP.

•Aug 10, 2015•1 citation

Entanglement Assisted Metrology

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Quantum information processing using localized ensembles of nuclear spins

Jacob M. Taylor, G. Giedke, H. Christ +5 more

We describe a technique for quantum information processing based on localized en sembles of nuclear spins. A qubit is identified as the presence or absence of a collective excitation of a mesoscopic ensemble of nuclear spins surrounding a single quantum dot. All single and two-qubit operations can be effected using hyperfine interactions and single-electron spin rotations, hence the proposed scheme avoids gate errors arising from entanglement between spin and orbital degrees of freedom. Ultra-long coherence times of nuclear spins suggest that this scheme could be particularly well suited for applications where long lived memory is essential.

arXiv:cond-mat/0407640•Jul 23, 2004•4 citations
This talk will illustrate the benefits offered by QIP with two devices which use quantum entanglement among nuclear spins to perform high-precision measurements: (1) a spin gyroscope that operates by detecting the frequency shift in the spins precession rate in the rotating frame, which is potentially more accurate than mechanical or optical devices; (2) a quantum amplifier which correlates the states of a macroscopic number of nuclear spins with the state of a single target spin, so that a collective measurement of the state of the amplifier’s spins reveals that of the target spin. Some potential implementations of these devices based on nuclear spins in naturally occurring materials will also be described.
We propose to implement a solid-state rotation sensor by employing a many-body quantum spin system which takes the advantages of the easy controllability of the electron spin and the robustness provided by the collective nuclear spin state. The sensor consists of a central electron spin coupled to many surrounding nuclear spins. Previously, this central spin system has been suggested to realize a quantum memory. Here, we further utilize the collective nuclear spins, which store a certain quantum state, to detect the macroscopic rotation. Different from other nuclear spin-based gyroscopes, our proposal does not directly manipulate nuclear spins via nuclear magnetic resonance technique. We analytically and numerically investigate the effects of partial nuclear polarization and decoherence on the sensitivity. We also briefly introduce the procedure to generate entanglement between nuclear spins through the quantum memory technique and to utilize this entanglement to enhance the sensing performance. Our proposal paves the way to the experimental realization of a compact solid-state, full-electrical, and spin-based gyroscope.
Quantum computers are machines that exploit the quantum mechanical properties of physical systems to realize an exponential speed-up in problem-solving capability compared with existing computers. Existing schemes for the realization of such machines occur in diverse areas such as atomic physics, nuclear magnetic resonance, superconductivity, quantum optics and solid state physics. We are concerned here with the experimental realization of various elements needed for quantum information processing using nuclear spin immersed in a confined electronic system in the quantum Hall regime. Some distinguishing characteristics of this approach include the application of the Overhauser effect for dynamic nuclear polarization at relatively high temperatures, spin measurement using relatively simple electrical detection techniques, spin control with microwave/radio frequency methods, the utilization of the electronic spin exciton as a possible mobile spin transfer mechanism for the eventual realization of a logic gate, and the application of semiconductor technology to device integration. Concepts involved in this approach are also illustrated with experimental results.
Nuclear Magnetic Resonance (NMR) forms a natural test-bed to perform quantum information processing (QIP) and has so far proven to be one of the most successful quantum information processors. The nuclear spins in a molecule treated as quantum bits or qubits which are the basic building blocks of a quantum computer. The development of NMR over half a century puts it in a platform where we can utilize its excellent control techniques over an ensemble of spin systems and perform quantum computation in a highly controlled way. Apart from a successful quantum information processor, NMR is also a highly powerful quantum platform where many of the potentially challenging quantum mechanical experiments can be performed.
The ability to perform quantum error correction (QEC) arbitrarily many cycles is a significant challenge for scalable quantum information processing (QIP). Key requirements for multiple-round QEC are a high degree of quantum control, the ability to efficiently characterize both intrinsic and extrinsic noise, and the ability to dynamically and efficiently extract entropy from ancilla qubits. Nuclear Magnetic Resonance (NMR) based quantum devices have demonstrated high control fidelity with up to 12 qubits, and the noise characterizations can be performed using an efficient protocol known as randomized benchmarking. One of the remaining challenges with NMR systems is that qubit initialization is normally only attainable via thermal equilibration. This results in very low polarizations in reasonable experimental conditions. Moving to electron-nuclear coupled spin systems in a single crystal is a promising solution to the ancilla qubit preparation problem. One obvious advantage of incorporating electron spins comes from higher gyromagnetic ratio of the electron which yields about three orders of magnitude larger thermal spin polarization than that of nuclear spins in the same experimental condition. In addition, fast control of nuclear spins is possible provided appropriate level of anisotropic hyperfine interaction strength. The nuclear spins can be polarized even beyond the thermal electron spin temperature using a technique Heat-Bath Algorithmic Cooling (HBAC). With theoretical ideas in hand, the next step is to develop classical instrumentations to control electron-nuclear coupled systems and accomplish high fidelity coherent control. Noise characterizations are also necessary for benchmarking the quality of control over the electron-nuclear spin system. \nI first present example applications of NMR QIP with small number of qubits: Testing a foundational question in quantum mechanics and measuring spectral density of noise in a quantum system. Then I report on our home-built X-band electron spin resonance (ESR) spectrometer and progress in achieving high fidelity coherent control of electron and nuclear spins for QIP. We focus on implementing nuclear spin manipulation via anisotropic hyperfine interaction and microwave (mw) control, but discussions also include electron nuclear double resonance (ENDOR) control techniques. We perform realistic algorithmic simulations to show that an experimental cooling of nuclear spins below electron thermal temperature is feasible, and to present the electron-nuclear spin systems as promising testbeds for scalable QIP.
We propose a new approach to the measurement of a single spin state, based on nuclear magnetic resonance (NMR) techniques and inspired by the coherent control over many-body systems envisaged by quantum information processing. A single target spin is coupled via the magnetic dipolar interaction to a large ensemble of spins. Applying radio frequency pulses, we can control the evolution so that the spin ensemble reaches one of two orthogonal states whose collective properties differ depending on the state of the target spin and are easily measured. We first describe this measurement process using quantum gates; then we show how equivalent schemes can be defined in terms of the Hamiltonian and thus implemented under conditions of real control, using well established NMR techniques. We demonstrate this method with a proof of principle experiment in ensemble liquid state NMR and simulations for small spin systems.
We describe a technique for quantum information processing based on localized en sembles of nuclear spins. A qubit is identified as the presence or absence of a collective excitation of a mesoscopic ensemble of nuclear spins surrounding a single quantum dot. All single and two-qubit operations can be effected using hyperfine interactions and single-electron spin rotations, hence the proposed scheme avoids gate errors arising from entanglement between spin and orbital degrees of freedom. Ultra-long coherence times of nuclear spins suggest that this scheme could be particularly well suited for applications where long lived memory is essential.