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Current noisy quantum computers have multiple types of errors, which can occur in the state preparation, measurement/readout, and gate operation, as well as intrinsic decoherence and relaxation. Partly motivated by the booming of intermediate-scale quantum processors, measurement and gate errors have been recently extensively studied, and several methods of mitigating them have been proposed and formulated in software packages (e.g., in IBM Qiskit). Despite this, the state preparation error and the procedure to quantify it have not yet been standardized, as state preparation and measurement errors are usually considered not directly separable. Inspired by a recent work of Laflamme, Lin, and Mor \cite{laflamme2022algorithmic}, we propose a simple and resource-efficient approach to quantify separately the state preparation and readout error rates. With these two errors separately quantified, we also propose methods to mitigate them separately, especially mitigating state preparation errors with linear (with the number of qubits) complexity. As a result of the separate mitigation, we show that the fidelity of the outcome can be improved by an order of magnitude compared to the standard measurement error mitigation scheme. We also show that the quantification and mitigation scheme is resilient against gate noise and can be immediately applied to current noisy quantum computers. To demonstrate this, we present results from cloud experiments on IBM's superconducting quantum computers. The results indicate that the state preparation error rate is also an important metric for qubit metrology that can be efficiently obtained. 

In quantum many-body spin systems, the interplay between the entangling effect of multiqubit Pauli measurements and the disentangling effect of single-qubit Pauli measurements may give rise to two competing effects. By introducing a randomized measurement pattern with such bases, a phase transition can be induced by altering the ratio between them. In this work, we numerically investigate a measurement-based model associated with the Fradkin-Shenker Hamiltonian that encompasses the deconfining, confining, and Higgs phases. We determine the phase diagram in our measurement-only model by employing entanglement measures. For the bulk topological order, we use the topological entanglement entropy. We also use the mutual information between separated boundary regions to diagnose the boundary phase transition associated with the Higgs or the bulk symmetry-protected topological (SPT) phase. We observe the structural similarity between our phase diagram and the one in the standard quantum Hamiltonian formulation of the Fradkin-Shenker model with the open rough boundary. First, a deconfining phase is detected by nonzero and constant topological entanglement entropy. Second, we find a (boundary) phase transition curve separating the Higgs=SPT phase from the rest. In certain limits, the topological phase transitions reside at the critical point of the formation of giant homological cycles in the bulk three-dimensional (3D) space-time lattice, as well as the bond percolation threshold of the boundary 2D space-time lattice when it is effectively decoupled from the bulk. Additionally, there are analogous mixed-phase properties at a certain region of the phase diagram, emerging from how we terminate the measurement-based procedure. Our findings pave an alternative pathway to study the physics of Higgs=SPT phases on quantum devices in the near future. 

National data have shown the need to expand and diversify the talent pool of the quantum technologies workforce. This article describes a newly designed 25-h summer quantum information science and technology (QIST) program for high school students in grades 10–12; the goal is to advance physical science literacy and diversify the STEM pipeline through novel quantum science and quantum computing access and learning. This partnership between Stony Brook University and the New York Hall of Science was designed by quantum physicists and physics education researchers. This manuscript describes the rationale and progression of quantum ideas and computing skills introduced in the outreach program. The program design scaffolded physics, mathematics, and computer science concepts to engage high school students in the excitement of quantum information science and technology fields. The disciplinary content included the limitations of classical computing, classical and quantum physics principles (diffraction, polarization, wave-particle duality), the Mach–Zehnder interferometer, superposition, quantum thought experiments (Schrödinger's cat and Wigner's friend), entanglement and Bell's inequality, quantum key distribution, and basic quantum computing skills. Students also spent time visiting laboratories and museum exhibits and learning about academic progressions and career pathways in quantum technologies. This university-based science outreach model may be replicated by other quantum educators and adapted for learning in formal contexts. 

[This paper is part of the Focused Collection in Investigating and Improving Quantum Education through Research.] There is a growing need in the United States for a workforce trained in quantum information science and technology (QIST), a disciplinary topic that is rarely addressed in precollege science, mathematics, and computer science curricula. University quantum physics and physics education researchers designed and initiated a 4-week, 12-h QIST professional development workshop for $N=51$preservice and in-service secondary school science, mathematics, and computer science educators. A STEM integration framework guided the workshop structure, which incorporated a situated cognition model for learning quantum concepts and computing, identifying recent advances in quantum technologies, planning curricula, and differentiating among QIST subfields including quantum communication, quantum computation, quantum simulation, and quantum metrology and sensing. The pre-/post-research design employed a newly developed teacher attitude survey, Exploratory factor analysis identified three latent constructs in teachers’ self-efficacy, including (i) knowledge about QIST academic pathways and careers; (ii) QIST pedagogical fluency and STEM integration; and (iii) facilitating QIST learning. Parametric comparisons of means indicated that teacher participants showed significant gains overall and in all latent constructs with medium to large effect sizes ( $p<0.001$). This professional learning model shows promise in strengthening teachers’ self-confidence in pedagogical content knowledge of quantum ideas so they may facilitate student engagement in quantum information science, a field that involves conceptual change and is often considered abstract, counterintuitive, inaccessible, and suitable only for the academically elite. Implications for policy and practice are discussed. Published by the American Physical Society2024 

[This paper is part of the Focused Collection in Investigating and Improving Quantum Education through Research.] With the current growth in quantum information science and technology (QIST), there is an increasing need to prepare precollege students for postsecondary QIST study and careers. This mixed methods, explanatory sequential research focused on students’ affective outcomes from a one-week, 25-h summer program for U.S. high school students in grades 10–12. The workshop structure was based upon psychosocial theories of self-determination and planned behavior, where QIST aspirations may be facilitated and viewed as achievable choices if students acquire disciplinary knowledge, self-efficacy, normative expectancy of their capacity in the field, and awareness of vocational roles. The program featured lectures, demonstrations, and hands-on experiences in classical and quantum physics and quantum computing. Students’ attitudes toward QIST ( $N=77$)—including self-efficacy, self-concept, relevance, career aspirations, and perceptions of quantitative fluency—showed improvement with a medium effect size, even though treatment students entered the program with more positive QIST attitudes when compared with a control group of high school physics students ( $N=65$). Postprogram interviews with $n=12$participants identified several explanatory themes: (i) Students tended to comprehend classical and quantum topics taught through multiple representations, regardless of whether they had taken physics previously; (ii) students experienced some challenges with mathematics and science concepts that support quantum understanding, yet they revealed a willingness to learn new concepts outside of their comfort zone; (iii) students expressed motivation for pursuing science, technology, engineering, and mathematics and/or quantum-related careers in the future, as well as increased QIST self-concept, largely through understanding the relevance of QIST in solving technological problems; and (iv) students reported increased self-efficacy in understanding QIST topics and performing related tasks. This informal summer program showed promise in promoting positive student attitudes toward QIST, a critical emerging field in advancing technological solutions for global challenges. Published by the American Physical Society2024 

Adaptive quantum circuits, which combine local unitary gates, midcircuit measurements, and feedforward operations, have recently emerged as a promising avenue for efficient state preparation, particularly on near-term quantum devices limited to shallow-depth circuits. Matrix product states (MPS) comprise a significant class of many-body entangled states, efficiently describing the ground states of one-dimensional gapped local Hamiltonians and finding applications in a number of recent quantum algorithms. Recently, it has been shown that the Affleck-Kennedy-Lieb-Tasaki state—a paradigmatic example of an MPS—can be exactly prepared with an adaptive quantum circuit of constant depth, an impossible feat with local unitary gates alone due to its nonzero correlation length [Smith , PRX Quantum 4, 020315 (2023)]. In this work, we broaden the scope of this approach and demonstrate that a diverse class of MPS can be exactly prepared using constant-depth adaptive quantum circuits, outperforming theoretically optimal preparation with unitary circuits. We show that this class includes short- and long-ranged entangled MPS, symmetry-protected topological (SPT) and symmetry-broken states, MPS with finite Abelian, non-Abelian, and continuous symmetries, resource states for MBQC, and families of states with tunable correlation length. Moreover, we illustrate the utility of our framework for designing constant-depth sampling protocols, such as for random MPS or for generating MPS in a particular SPT phase. We present sufficient conditions for particular MPS to be preparable in constant time, with global on-site symmetry playing a pivotal role. Altogether, this work demonstrates the immense promise of adaptive quantum circuits for efficiently preparing many-body entangled states and provides explicit algorithms that outperform known protocols to prepare an essential class of states.