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Rydberg atom data register: A use of atomic electronic states for information storage

Jaewook Ahn

Published Jan 1, 2002• 0 citations
OpenAlex

Abstract

Quantum computation has experienced a steady growth in interest in recent years. With the rapid development of quantum technologies, the quantum mechanical nature of physical systems is becoming an increasingly important part of future industrial technology. The Rydberg atom is one of the best test tubes in which to attempt programmable coherent control because of our in-depth understanding of both atomic physics and ultrafast optics. We demonstrate the use of Rydberg atoms for processing quantum information and implementing quantum algorithms. We adopted N Rydberg energy levels of Cesium atom to store information. The phases of the energy states were each programmed and coherently evolve in time with the encoded information. A coherent manipulation then transferred the information contained in the phases to state amplitudes. The programming and the converting of the information in the data register were both performed by ultrafast optical pulses. We implemented an N-state Rydberg atom data register, with N = 6 and 8. Using half-cycle pulses (HCP), we devised methods which perform unitary operations on this data register. Application of the HCP, or terahertz short pulse, to wave packets prepared with one energy state phase-reversed with respect to the others yields a much simpler wave packet. This interaction forced multi-mode interference which constructively interfered only for the phase-flipped state. An impulsive model calculation as well as direct integration of the time-dependent Schrodinger equation showed good agreement with the experimental data. Related to the quantum algorithms, the pseudo-unitary operation implemented by the HCP had a similar structural form to the Grover's inversion-about-average operation. For the same reasons that lead to the Grover's quantum state amplification, the state amplitude of the energy state whose phase was reversed robbed atomic population from all other states. Our implementation of the Grover's inversion-about-average operation has accomplished most of Grover's search protocol. In order to improve upon our implementation and to attempt other quantum algorithms, we conclude that a sophisticated shaping of terahertz pulses is required.

Related papers

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A terahertz half-cycle pulse was used to retrieve information stored as quantum phase in an N-state Rydberg atom data register. The register was prepared as a wave packet with one state phase reversed from the others (the "marked bit"). A half-cycle pulse then drove a significant portion of the electron probability into the flipped state via multimode interference.

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The field of coherent control has today been seeing significant progress, in a wide array of physical systems. One such system is the Rydberg atom. The long lifetime, strong dipole interactions, multiple degrees of freedom, and simple atomic structure make Rydberg atoms particularly appealing for experiments involving coherent control. The same properties have led to the exploration of Rydberg atoms as candidates for quantum information storage, processing and retrieval. Quantum information processing is a particular application of coherent control. Rather than being disparate subjects of study, coherent control of Rydberg atoms and processing of information stored as phase in different Rydberg levels are two sides of the same coin. In this dissertation, we experimentally characterize the effect of a half-cycle pulse on the phases of the states of a Rydberg wave packet and their mutual coherence. This has bearing both on our ability to control the states of the atom and on our ability to measure the information stored as quantum phase. We observe delay dependent phase shifts and losses of coherence. Despite a loss of information due to transfer of quantum amplitude to states outside the data register, we demonstrate partial retrieval of that information by the application of a second half cycle pulse. We also present an essential states model of the interaction, and we compare results from the model to experimental features observed. Although the particulars may vary, the concepts involved are quite general and may be applied to multilevel systems other than Rydberg atoms.

•Jan 1, 2006•0 citations

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Jaewook Ahn, T. C. Weinacht, P. H. Bucksbaum

Information was stored as quantum phase in an N-state Rydberg atom data register. One or more flipped states stored in an eight-state atomic wave packet could be retrieved in a single operation, in agreement with a recent proposal by Grover.

Science•Jan 21, 2000•286 citations
Quantum computation has experienced a steady growth in interest in recent years. With the rapid development of quantum technologies, the quantum mechanical nature of physical systems is becoming an increasingly important part of future industrial technology. The Rydberg atom is one of the best test tubes in which to attempt programmable coherent control because of our in-depth understanding of both atomic physics and ultrafast optics. We demonstrate the use of Rydberg atoms for processing quantum information and implementing quantum algorithms. We adopted N Rydberg energy levels of Cesium atom to store information. The phases of the energy states were each programmed and coherently evolve in time with the encoded information. A coherent manipulation then transferred the information contained in the phases to state amplitudes. The programming and the converting of the information in the data register were both performed by ultrafast optical pulses. We implemented an N-state Rydberg atom data register, with N = 6 and 8. Using half-cycle pulses (HCP), we devised methods which perform unitary operations on this data register. Application of the HCP, or terahertz short pulse, to wave packets prepared with one energy state phase-reversed with respect to the others yields a much simpler wave packet. This interaction forced multi-mode interference which constructively interfered only for the phase-flipped state. An impulsive model calculation as well as direct integration of the time-dependent Schrodinger equation showed good agreement with the experimental data. Related to the quantum algorithms, the pseudo-unitary operation implemented by the HCP had a similar structural form to the Grover's inversion-about-average operation. For the same reasons that lead to the Grover's quantum state amplification, the state amplitude of the energy state whose phase was reversed robbed atomic population from all other states. Our implementation of the Grover's inversion-about-average operation has accomplished most of Grover's search protocol. In order to improve upon our implementation and to attempt other quantum algorithms, we conclude that a sophisticated shaping of terahertz pulses is required.
Summary form only given. Optical pulse shaping and wave-packet holography have been used to store information in the phase of an atomic Rydberg wave-packet. We present a new method of retrieving this phase information by using a terahertz domain half-cycle pulse (HCP) to coherently redistribute the Rydberg population. We use programmed optical pulses to create radial wave-packets in a beam of atomic Cs centered at n = 26p with one state phase-reversed from the others. An impulse model for this atom-HCP interaction is employed to qualitatively explain this flipped-state amplification.
We analyze a quantum search protocol to retrieve phase information from a Rydberg-atom data register using a subpicosecond half-cycle electric field pulse. Calculations show that the half-cycle pulse can perform the phase retrieval only within a range of peak field values. By varying the phases of the constituent orbitals of the Rydberg wave packet register, we demonstrate coherent control of the phase retrieval process. By specially programming the phases of the orbitals comprising the initial wave packet, we show that it is possible to use the search method as a way to synthesize single energy eigenstates.
The field of coherent control has today been seeing significant progress, in a wide array of physical systems. One such system is the Rydberg atom. The long lifetime, strong dipole interactions, multiple degrees of freedom, and simple atomic structure make Rydberg atoms particularly appealing for experiments involving coherent control. The same properties have led to the exploration of Rydberg atoms as candidates for quantum information storage, processing and retrieval. Quantum information processing is a particular application of coherent control. Rather than being disparate subjects of study, coherent control of Rydberg atoms and processing of information stored as phase in different Rydberg levels are two sides of the same coin. In this dissertation, we experimentally characterize the effect of a half-cycle pulse on the phases of the states of a Rydberg wave packet and their mutual coherence. This has bearing both on our ability to control the states of the atom and on our ability to measure the information stored as quantum phase. We observe delay dependent phase shifts and losses of coherence. Despite a loss of information due to transfer of quantum amplitude to states outside the data register, we demonstrate partial retrieval of that information by the application of a second half cycle pulse. We also present an essential states model of the interaction, and we compare results from the model to experimental features observed. Although the particulars may vary, the concepts involved are quite general and may be applied to multilevel systems other than Rydberg atoms.