By leveraging shared entanglement between a pair of qubits, one can teleport a quantum state from one particle to another. Recent advances have uncovered an intrinsically many-body generalization of quantum teleportation, with an elegant and surprising connection to gravity. In particular, the teleportation of quantum information relies on many-body dynamics, which originate from strongly-interacting systems that are holographically dual to gravity; from the gravitational perspective, such quantum teleportation can be understood as the transmission of information through a traversable wormhole. Here, we propose and analyze a new mechanism for many-body quantum teleportation -- dubbed peaked-size teleportation. Intriguingly, peaked-size teleportation utilizes precisely the same type of quantum circuit as traversable wormhole teleportation, yet has a completely distinct microscopic origin: it relies upon the spreading of local operators under generic thermalizing dynamics and not gravitational physics. We demonstrate the ubiquity of peaked-size teleportation, both analytically and numerically, across a diverse landscape of physical systems, including random unitary circuits, the Sachdev-Ye-Kitaev model (at high temperatures), one-dimensional spin chains and a bulk theory of gravity with stringy corrections. Our results pave the way towards using many-body quantum teleportation as a powerful experimental tool for: (i) characterizing the size distributions of operators in strongly-correlated systems and (ii) distinguishing between generic and intrinsically gravitational scrambling dynamics. To this end, we provide a detailed experimental blueprint for realizing many-body quantum teleportation in both trapped ions and Rydberg atom arrays; effects of decoherence and experimental imperfections are analyzed.

%B Physical Review X %V 12 %8 8/5/2022 %G eng %U https://arxiv.org/abs/2102.00010 %R 10.1103/physrevx.12.031013 %0 Journal Article %D 2021 %T Cross-Platform Comparison of Arbitrary Quantum Computations %A Daiwei Zhu %A Ze-Pei Cian %A Crystal Noel %A Andrew Risinger %A Debopriyo Biswas %A Laird Egan %A Yingyue Zhu %A Alaina M. Green %A Cinthia Huerta Alderete %A Nhung H. Nguyen %A Qingfeng Wang %A Andrii Maksymov %A Yunseong Nam %A Marko Cetina %A Norbert M. Linke %A Mohammad Hafezi %A Christopher Monroe %XAs we approach the era of quantum advantage, when quantum computers (QCs) can outperform any classical computer on particular tasks, there remains the difficult challenge of how to validate their performance. While algorithmic success can be easily verified in some instances such as number factoring or oracular algorithms, these approaches only provide pass/fail information for a single QC. On the other hand, a comparison between different QCs on the same arbitrary circuit provides a lower-bound for generic validation: a quantum computation is only as valid as the agreement between the results produced on different QCs. Such an approach is also at the heart of evaluating metrological standards such as disparate atomic clocks. In this paper, we report a cross-platform QC comparison using randomized and correlated measurements that results in a wealth of information on the QC systems. We execute several quantum circuits on widely different physical QC platforms and analyze the cross-platform fidelities.

%8 7/27/2021 %G eng %U https://arxiv.org/abs/2107.11387 %0 Journal Article %D 2020 %T Quantum walks and Dirac cellular automata on a programmable trapped-ion quantum computer %A C. Huerta Alderete %A Shivani Singh %A Nhung H. Nguyen %A Daiwei Zhu %A Radhakrishnan Balu %A Christopher Monroe %A C. M. Chandrashekar %A Norbert M. Linke %XThe quantum walk formalism is a widely used and highly successful framework for modeling quantum systems, such as simulations of the Dirac equation, different dynamics in both the low and high energy regime, and for developing a wide range of quantum algorithms. Here we present the circuit-based implementation of a discrete-time quantum walk in position space on a five-qubit trapped-ion quantum processor. We encode the space of walker positions in particular multi-qubit states and program the system to operate with different quantum walk parameters, experimentally realizing a Dirac cellular automaton with tunable mass parameter. The quantum walk circuits and position state mapping scale favorably to a larger model and physical systems, allowing the implementation of any algorithm based on discrete-time quantum walks algorithm and the dynamics associated with the discretized version of the Dirac equation.

%8 2/6/2020 %G eng %U https://arxiv.org/abs/2002.02537 %0 Journal Article %D 2020 %T Universal one-dimensional discrete-time quantum walks and their implementation on near term quantum hardware %A Shivani Singh %A Cinthia H. Alderete %A Radhakrishnan Balu %A Christopher Monroe %A Norbert M. Linke %A C. M. Chandrashekar %XQuantum walks are a promising framework for developing quantum algorithms and quantum simulations. Quantum walks represent an important test case for the application of quantum computers. Here we present different forms of discrete-time quantum walks and show their equivalence for physical realizations. Using an appropriate digital mapping of the position space on which a walker evolves onto the multi-qubit states in a quantum processor, we present different configurations of quantum circuits for the implementation of discrete-time quantum walks in one-dimensional position space. With example circuits for a five qubit machine we address scalability to higher dimensions and larger quantum processors.

%8 1/30/2020 %G eng %U https://arxiv.org/abs/2001.11197 %0 Journal Article %D 2019 %T Toward convergence of effective field theory simulations on digital quantum computers %A Omar Shehab %A Kevin A. Landsman %A Yunseong Nam %A Daiwei Zhu %A Norbert M. Linke %A Matthew J. Keesan %A Raphael C. Pooser %A Christopher R. Monroe %XWe report results for simulating an effective field theory to compute the binding energy of the deuteron nucleus using a hybrid algorithm on a trapped-ion quantum computer. Two increasingly complex unitary coupled-cluster ansaetze have been used to compute the binding energy to within a few percent for successively more complex Hamiltonians. By increasing the complexity of the Hamiltonian, allowing more terms in the effective field theory expansion and calculating their expectation values, we present a benchmark for quantum computers based on their ability to scalably calculate the effective field theory with increasing accuracy. Our result of E4=−2.220±0.179MeV may be compared with the exact Deuteron ground-state energy −2.224MeV. We also demonstrate an error mitigation technique using Richardson extrapolation on ion traps for the first time. The error mitigation circuit represents a record for deepest quantum circuit on a trapped-ion quantum computer.

%8 04/18/2019 %G eng %U https://arxiv.org/abs/1904.04338 %0 Journal Article %D 2019 %T Two-qubit entangling gates within arbitrarily long chains of trapped ions %A Kevin A. Landsman %A Yukai Wu %A Pak Hong Leung %A Daiwei Zhu %A Norbert M. Linke %A Kenneth R. Brown %A Luming Duan %A Christopher R. Monroe %XIon trap systems are a leading platform for large scale quantum computers. Trapped ion qubit crystals are fully-connected and reconfigurable, owing to their long range Coulomb interaction that can be modulated with external optical forces. However, the spectral crowding of collective motional modes could pose a challenge to the control of such interactions for large numbers of qubits. Here, we show that high-fidelity quantum gate operations are still possible with very large trapped ion crystals, simplifying the scaling of ion trap quantum computers. To this end, we present analytical work that determines how parallel entangling gates produce a crosstalk error that falls off as the inverse cube of the distance between the pairs. We also show experimental work demonstrating entangling gates on a fully-connected chain of seventeen 171Yb+ ions with fidelities as high as 97(1)%.

%8 05/28/2019 %G eng %U https://arxiv.org/abs/1905.10421 %0 Journal Article %D 2018 %T Demonstration of Bayesian quantum game on an ion trap quantum computer %A Neal Solmeyer %A Norbert M. Linke %A Caroline Figgatt %A Kevin A. Landsman %A Radhakrishnan Balu %A George Siopsis %A Christopher Monroe %XWe demonstrate a Bayesian quantum game on an ion trap quantum computer with five qubits. The players share an entangled pair of qubits and perform rotations on their qubit as the strategy choice. Two five-qubit circuits are sufficient to run all 16 possible strategy choice sets in a game with four possible strategies. The data are then parsed into player types randomly in order to combine them classically into a Bayesian framework. We exhaustively compute the possible strategies of the game so that the experimental data can be used to solve for the Nash equilibria of the game directly. Then we compare the payoff at the Nash equilibria and location of phase-change-like transitions obtained from the experimental data to the theory, and study how it changes as a function of the amount of entanglement.

%G eng %U https://arxiv.org/abs/1802.08116 %0 Journal Article %J J. Phys. B: At. Mol. Opt. Phys. %D 2018 %T Machine learning assisted readout of trapped-ion qubits %A Alireza Seif %A Kevin A. Landsman %A Norbert M. Linke %A Caroline Figgatt %A C. Monroe %A Mohammad Hafezi %XWe reduce measurement errors in a quantum computer using machine learning techniques. We exploit a simple yet versatile neural network to classify multi-qubit quantum states, which is trained using experimental data. This flexible approach allows the incorporation of any number of features of the data with minimal modifications to the underlying network architecture. We experimentally illustrate this approach in the readout of trapped-ion qubits using additional spatial and temporal features in the data. Using this neural network classifier, we efficiently treat qubit readout crosstalk, resulting in a 30\% improvement in detection error over the conventional threshold method. Our approach does not depend on the specific details of the system and can be readily generalized to other quantum computing platforms.

%B J. Phys. B: At. Mol. Opt. Phys. %V 51 %8 2018/05/01 %G eng %U https://arxiv.org/abs/1804.07718 %& 174006 %R https://doi.org/10.1088/1361-6455/aad62b %0 Journal Article %J Physical Review Letters %D 2018 %T Robust two-qubit gates in a linear ion crystal using a frequency-modulated driving force %A Pak Hong Leung %A Kevin A. Landsman %A Caroline Figgatt %A Norbert M. Linke %A Christopher Monroe %A Kenneth R. Brown %XIn an ion trap quantum computer, collective motional modes are used to entangle two or more qubits in order to execute multi-qubit logical gates. Any residual entanglement between the internal and motional states of the ions will result in decoherence errors, especially when there are many spectator ions in the crystal. We propose using a frequency-modulated (FM) driving force to minimize such errors and implement it experimentally. In simulation, we obtained an optimized FM gate that can suppress decoherence to less than 10−4 and is robust against a frequency drift of more than ±1 kHz. The two-qubit gate was tested in a five-qubit trapped ion crystal, with 98.3(4)% fidelity for a Mølmer-Sørensen entangling gate and 98.6(7)% for a controlled-not (CNOT) gate. We also show an optimized FM two-qubit gate for 17 ions, proving the scalability of our method.

%B Physical Review Letters %V 120 %P 020501 %8 2018/01/09 %G eng %U https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.020501 %N 2 %R 10.1103/PhysRevLett.120.020501 %0 Journal Article %D 2018 %T Verified Quantum Information Scrambling %A Kevin A. Landsman %A Caroline Figgatt %A Thomas Schuster %A Norbert M. Linke %A Beni Yoshida %A Norman Y. Yao %A Christopher Monroe %XQuantum scrambling is the dispersal of local information into many-body quantum entanglements and correlations distributed throughout the entire system. This concept underlies the dynamics of thermalization in closed quantum systems, and more recently has emerged as a powerful tool for characterizing chaos in black holes. However, the direct experimental measurement of quantum scrambling is difficult, owing to the exponential complexity of ergodic many-body entangled states. One way to characterize quantum scrambling is to measure an out-of-time-ordered correlation function (OTOC); however, since scrambling leads to their decay, OTOCs do not generally discriminate between quantum scrambling and ordinary decoherence. Here, we implement a quantum circuit that provides a positive test for the scrambling features of a given unitary process. This approach conditionally teleports a quantum state through the circuit, providing an unambiguous litmus test for scrambling while projecting potential circuit errors into an ancillary observable. We engineer quantum scrambling processes through a tunable 3-qubit unitary operation as part of a 7-qubit circuit on an ion trap quantum computer. Measured teleportation fidelities are typically ∼80%, and enable us to experimentally bound the scrambling-induced decay of the corresponding OTOC measurement.

%G eng %U https://arxiv.org/abs/1806.02807