Extrinsic interference is routinely faced in systems engineering, and a common solution is to rely on a broad class of filtering techniques to a ord stability to intrinsically unstable systems or isolate particular signals from a noisy background. Experimentalists leading the development of a new generation of quantum-enabled technologies similarly encounter time-varying noise in realistic laboratory settings. They face substantial challenges in either suppressing such noise for high-fidelity quantum operations 1 or controllably exploiting it in quantum-enhanced sensing [2][3][4] or system identification tasks 5,6 , due to a lack of e cient, validated approaches to understanding and predicting quantum dynamics in the presence of realistic time-varying noise. In this work we use the theory of quantum control engineering . We demonstrate the utility of these constructs for directly predicting the evolution of a quantum state in a realistic noisy environment as well as for developing novel robust control and sensing protocols. These experiments provide a significant advance in our understanding of the physics underlying controlled quantum dynamics, and unlock new capabilities for the emerging field of quantum systems engineering.Time-varying noise coupled to quantum systems-typically qubits-generically results in decoherence, or a loss of 'quantumness' of the system. Broadly, one may think of the state of the quantum system becoming randomized through uncontrolled (and often uncontrollable) interactions with the environment during both idle periods and active control operations (Fig. 1a). Despite the ubiquity of this phenomenon, it is a challenging problem to predict the average evolution of a qubit state undergoing a specific, but arbitrary operation in the presence of realistic time-dependent noise-how much randomization does one expect and how well can one perform the target operation? Making such predictions accurately is precisely the capability that experimentalists require in realistic laboratory settings. Moreover, this capability is fundamental to the development of novel control techniques designed to modify or suppress decoherence as researchers attempt to build quantum-enabled technologies for applications such as quantum information and quantum sensing.These considerations motivate the development of novel engineering-inspired analytic tools enabling a user to accurately predict the behaviour of a controlled quantum system in realistic laboratory environments. Recent work has demonstrated that the average dynamics of a controlled qubit state evolution may be captured using filter-transfer functions (FFs) characterizing the control. The fidelity of an arbitrary operation over duration τ ,, is degraded owing to frequency-domain spectral overlap between noise in the environment given by a power spectrum S(ω), and the filter-transfer functions denoted F(ω) (Methods) [11][12][13][14] . The FF description of ensemble-average quantum dynamics tremendously simplifies the task of analysing the expected performa...

Many schemes for implementing quantum information processing require that the atomic states used have a nonzero magnetic moment; however, such magnetically sensitive states of an atom are vulnerable to decoherence due to fluctuating magnetic fields. Dressing an atom with external fields is a powerful method of reducing such decoherence [N. Timoney et al., Nature (London) 476, 185 (2011)]. We introduce an experimentally simpler method of manipulating such a dressed-state qubit, which allows the implementation of general rotations of the qubit, and demonstrate this method using a trapped ytterbium ion.

This version is available from Sussex Research Online: http://sro.sussex.ac.uk/38820/ This document is made available in accordance with publisher policies and may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the URL above for details on accessing the published version. Copyright and reuse:Sussex Research Online is a digital repository of the research output of the University.Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available.Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. We present the design and operation of an ytterbium ion trap experiment with a setup offering versatile optical access and 90 electrical interconnects that can host advanced surface and multilayer ion trap chips mounted on chip carriers. We operate a macroscopic ion trap compatible with this chip carrier design and characterize its performance, demonstrating secular frequencies >1 MHz, and trap and cool nearly all of the stable isotopes, including 171 Yb + ions, as well as ion crystals. For this particular trap we measure the motional heating rate ṅ and observe an ṅ ∝1/ω 2 behavior for different secular frequencies ω. We also determine a spectral noise density S E (1 MHz) = 3.6(9) × 10 −11 V 2 m −2 Hz −1 at an ion electrode spacing of 310(10) µm. We describe the experimental setup for trapping and cooling Yb + ions and provide frequency measurements of the 2 S 1/2 ↔ 2 P 1/2 and 2 D 3/2 ↔ 3 D[3/2] 1/2 transitions for the stable 170 Yb + , 171 Yb + , 172 Yb + , 174 Yb + ,a n d 176 Yb + isotopes which are more precise than previously published work.