Preparation of Entangled States through Hilbert Space Engineering

Lin, Yiheng; Gaebler, John; Reiter, Florentin; Tan, Ting Rei; Bowler, Ryan; Wan, Yong; Keith, Adam C.; Knill, Emanuel; Glancy, Scott; Coakley, Kevin J.; Sørensen, Anders S.; Leibfried, D.; Wineland, David J.

doi:10.1103/physrevlett.117.140502

Cited by 40 publications

(35 citation statements)

References 48 publications

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“…A refinement of the ML analysis is required to reduce the number of parameters needed for the q j (c) and the complexity of the algorithms. For this, we bin the counts into seven bins of consecutive counts [37]. The binning is done separately by setting aside a random 10 % of each reference histogram and using this as a training set to determine a binning that maximizes state information quantified by a mutual-information-based heuristic.…”

Section: State Detection and Tomographymentioning

confidence: 99%

High-Fidelity Universal Gate Set forBe9+Ion Qubits

et al. 2016

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We report high-fidelity laser-beam-induced quantum logic gates on magnetic-field-insensitive qubits comprised of hyperfine states in 9 Be + ions with a memory coherence time of more than 1 s. We demonstrate single-qubit gates with error per gate of 3.8(1) × 10 −5 . By creating a Bell state with a deterministic two-qubit gate, we deduce a gate error of 8(4) × 10 −4 . We characterize the errors in our implementation and discuss methods to further reduce imperfections towards values that are compatible with fault-tolerant processing at realistic overhead.Quantum computers can solve certain problems that are thought to be intractable on conventional computers. An important general goal is to realize universal quantum information processing (QIP), which could be used for algorithms having a quantum advantage over processing with conventional bits as well as to simulate other quantum systems of interest [1][2][3]. For large problems, it is generally agreed that individual logic gate errors must be reduced below a certain threshold, often taken to be around 10 −4 [4][5][6], to achieve fault tolerance without excessive overhead in the number of physical qubits required to implement a logical qubit. This level has been achieved in some experiments for all elementary operations including state preparation and readout, with the exception of two-qubit gates, emphasizing the importance of improving multi-qubit gate fidelities. [7,8]. As various ions differ in mass, electronic, and hyperfine structure, they each have technical advantages and disadvantages. For example, 9 Be + is the lightest ion currently considered for QIP, and as such, has several potential advantages. The relatively light mass yields deeper traps and higher motional frequencies for given applied potentials, and facilitates fast ion transport [9,10]. Light mass also yields stronger laser-induced effective spin-spin coupling (inversely proportional to the mass), which can yield less spontaneous emission error for a given laser intensity [11]. However, a disadvantage of 9 Be + ion qubits compared to some heavier ions such as 40 Ca + and 43 Ca + [12, 13] has been the difficulty of producing and controlling the ultraviolet (313 nm) light required to drive 9 Be + stimulated-Raman transitions. In the work reported here, we use an ion trap array designed for scalable QIP [14] and take advantage of recent technological developments with lasers and optical fibers that improve beam quality and pointing stability. We also implement active control of laser pulse intensities to re- duce errors. We demonstrate laser-induced single-qubit computational gate errors of 3.8(1) × 10 −5 and realize a deterministic two-qubit gate to ideally produce the Bell state |Φ + = 1 √ 2 (|↑↑ + |↓↓ ). By characterizing the effects of known error sources with numerical simulations and calibration measurements, we deduce an entangling gate infidelity or error of = 8(4) × 10 −4 , where = 1 -F, and F is the fidelity. Along with Ref.[13]; these appear to be the highest two-qubit gate fidelitie...

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Section: State Detection and Tomographymentioning

confidence: 99%

High-Fidelity Universal Gate Set forBe9+Ion Qubits

et al. 2016

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“…The first example we consider is in the context of dissipative state preparation [77][78][79][80][81]. The general goal here is to engineer dissipative couplings such that the interplay between driving and dissipation leads an open quantum system to an interesting target steady state ρ ss = ρ S (t → ∞).…”

Section: A Dissipative Dimer Formationmentioning

confidence: 99%

Implementation of chiral quantum optics with Rydberg and trapped-ion setups

et al. 2016

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We propose two setups for realizing a chiral quantum network, where two-level systems representing the nodes interact via directional emission into discrete waveguides, as introduced in T. Ramos et al. [Phys. Rev. A 93, 062104 (2016)]. The first implementation realizes a spin waveguide via Rydberg states in a chain of atoms, whereas the second one realizes a phonon waveguide via the localized vibrations of a string of trapped ions. For both architectures, we show that strong chirality can be obtained by a proper design of synthetic gauge fields in the couplings from the nodes to the waveguide. In the Rydberg case, this is achieved via intrinsic spin-orbit coupling in the dipole-dipole interactions, while for the trapped ions it is obtained by engineered sideband transitions. We take long-range couplings into account that appear naturally in these implementations, discuss useful experimental parameters, and analyze potential error sources. Finally, we describe effects that can be observed in these implementations within state-of-the-art technology, such as the driven-dissipative formation of entangled dimer states.

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“…Quantum state preparation is a prominent routine in quantum information processing toolbox [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Such procedure often implies steering a quantum system from a "simple" towards a more complex, pre-designated resourceful state, e.g.…”

Section: Introductionmentioning

confidence: 99%

Measurement-driven navigation in many-body Hilbert space: Active-decision steering

Herasymenko¹,

Gornyi²,

Gefen³

2021

Preprint

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The challenge of preparing a system in a designated state spans diverse facets of quantum mechanics. To complete this task of steering quantum states, one can employ quantum control through a sequence of generalized measurements which direct the system towards the target state. In an active version of this protocol, the obtained measurement readouts are used to adjust the protocol on-the-go, with a possibility for accelerated performance or fidelity increase. In this work, we consider such active measurement-driven steering as applied to the challenging case of many-body quantum systems. The target states of highest interest would be those with multipartite entanglement. Such state preparation in a measurement-based protocol is limited by the natural constraints for system-detector couplings. We develop a framework for finding such physically feasible couplings, based on parent Hamiltonian construction. For helpful decision-making strategies, we offer Hilbert-space-orientation techniques, comparable to those used in navigation. The first one is to tie the active-decision protocol to the fastest accumulation of the cost function, such as the target state fidelity. We show the potential of 9.5-fold speedup, employing this approach for generating the ground state of the Affleck-Lieb-Kennedy-Tasaki spin chain. The second wayfinding technique is to map out the available measurement actions onto a Quantum State Machine. A decision-making protocol can be based on such a representation, using semiclassical heuristics. This approach has advantages and limitations complementary to the cost function-based method. We give an example of a W-state preparation which is accelerated with this method by a factor of 12.5.

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Preparation of Entangled States through Hilbert Space Engineering

Cited by 40 publications

References 48 publications

High-Fidelity Universal Gate Set forBe9+Ion Qubits

High-Fidelity Universal Gate Set forBe9+Ion Qubits

Implementation of chiral quantum optics with Rydberg and trapped-ion setups

Measurement-driven navigation in many-body Hilbert space: Active-decision steering

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