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arXiv:1406.5821 · Journal of Physics B Atomic Molecular and Optical Physics

State selective detection of hyperfine qubits

Sabine Wölk, Christian Piltz, Theeraphot Sriarunothai, Christof Wunderlich

Published Mar 17, 2015• 24 citations
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Abstract

Abstract In order to faithfully detect the state of an individual two-state quantum system (qubit) realized using, for example, a trapped ion or atom, state selective scattering of resonance fluorescence is well established. The simplest way to read out this measurement and assign a state is the threshold method. The detection error can be decreased by using more advanced detection methods like the time-resolved method (Myerson et al 2008 Phys. Rev. Lett. 100 200502 ) or the π -pulse detection method (Hemmerling et al 2012 New. J. Phys. 14 023043 ). These methods were introduced to qubits with a single possible state change during the measurement process. However, there exist many qubits like the hyperfine qubit of where several state change are possible. To decrease the detection error for such qubits, we develop generalizations of the time-resolved method and the π -pulse detection method for such qubits. We show the advantages of these generalized detection methods in numerical simulations and experiments using the hyperfine qubit of . The generalized detection methods developed here can be implemented in an efficient way such that experimental real time state discrimination with improved fidelity is possible.

DOI
10.1088/0953-4075/48/7/075101

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Abstract In order to faithfully detect the state of an individual two-state quantum system (qubit) realized using, for example, a trapped ion or atom, state selective scattering of resonance fluorescence is well established. The simplest way to read out this measurement and assign a state is the threshold method. The detection error can be decreased by using more advanced detection methods like the time-resolved method (Myerson et al 2008 Phys. Rev. Lett. 100 200502 ) or the π -pulse detection method (Hemmerling et al 2012 New. J. Phys. 14 023043 ). These methods were introduced to qubits with a single possible state change during the measurement process. However, there exist many qubits like the hyperfine qubit of where several state change are possible. To decrease the detection error for such qubits, we develop generalizations of the time-resolved method and the π -pulse detection method for such qubits. We show the advantages of these generalized detection methods in numerical simulations and experiments using the hyperfine qubit of . The generalized detection methods developed here can be implemented in an efficient way such that experimental real time state discrimination with improved fidelity is possible.
In order to faithfully detect the state of an individual two-state quantum system (qubit) realized using, for example, a trapped ion or atom, state selective scattering of resonance fluorescence is well established.The simplest way to read out this measurement and assign a state is the threshold method.The detection error can be decreased by using more advanced detection methods like the time-resolved method [1] or the π-pulse detection method [2].These methods were introduced to qubits with a single possible state change during the measurement process.However, there exist many qubits like the hyperfine qubit of 171 Y b + where several state change are possible.To decrease the detection error for such qubits, we develope generalizations of the time-resolved method and the π-pulse detection method for such qubits.We show the advantages of these generalized detection methods in numerical simulations and experiments using the hyperfine qubit of 171 Y b + .The generalized detection methods developed here can be implemented in an efficient way such that experimental real time state discrimination with improved fidelity is possible.
Abstract Short pulses from mode-locked lasers can produce background-free atomic fluorescence by allowing temporal separation of the prompt incidental scatter from the subsequent atomic emission. We use this to improve our quantum state detection of optical-frequency and electron-shelved trapped ion qubits by more than two orders of magnitude. For direct detection of qubits defined on atomic hyperfine structure, however, the large bandwidth of short pulses is greater than the hyperfine splitting, and repeated excitation is not qubit state selective. Here, we show that the state resolution needed for projective quantum measurement of hyperfine qubits can be recovered by applying techniques from coherent control to the orbiting valence electron of the queried ion. We demonstrate electron wavepacket interference to allow readout of the original qubit state using broadband pulses, even in the presence of large amounts of background laser scatter.
Simultaneous measurement of multiple qubits stored in hyperfine levels of trapped 111Cd+ ions is realized with an intensified charge-coupled device (CCD) imager. A general theory of fluorescence detection for hyperfine qubits is presented and applied to experimental data. The use of an imager for photon detection allows for multiple qubit state measurement with detection fidelities of greater than 98%. Improvements in readout speed and fidelity are discussed in the context of scalable quantum computation architectures.
Fast and efficient detection of the qubit state in trapped ion systems is critical for implementing quantum error correction and performing fundamental tests such as a loophole-free Bell test. In this work we present a simple qubit state detection protocol for a (171)Yb+ hyperfine atomic qubit trapped in a microfabricated surface trap, enabled by high collection efficiency of the scattered photons and low background photon count rate. We demonstrate average detection times of 10.5, 28.1, and 99.8 μs, corresponding to state detection fidelities of 99%, 99.856(8)%, and 99.915(7)%, respectively.
Simultaneous measurement of multiple qubits stored in hyperfine levels of trapped ^{111}Cd^+ ions is realized with an intensified charge-coupled device (CCD) imager. A general theory of fluorescence detection for hyperfine qubits is presented and applied to experimental data. The use of an imager for photon detection allows for multiple qubit state measurement with detection fidelities of greater than 98%98\%98%. Improvements in readout speed and fidelity are discussed in the context of scalable quantum computation architectures.
Simultaneous measurement of multiple qubits stored in hyperfine levels of trapped 111Cd+ ions is realized with an intensified charge-coupled device (CCD) imager. A general theory of fluorescence detection for hyperfine qubits is presented and applied to experimental data. The use of an intensified CCD for photon detection allows for multiple qubit state measurement with detection fidelities of greater than 98%. Improvements in readout speed and fidelity are discussed in the context of scalable quantum computation architectures.