Quantum 5, 561 (2021). https://doi.org/10.22331/q-2021-10-07-561 Entanglement in symmetric quantum states and the theory of copositive matrices are intimately related concepts. For the simplest symmetric states, i.e., the diagonal symmetric (DS) states, it has been shown […]
Quantum 5, 560 (2021). https://doi.org/10.22331/q-2021-10-07-560 A leading proposal for verifying near-term quantum supremacy experiments on noisy random quantum circuits is linear cross-entropy benchmarking. For a quantum circuit $C$ on $n$ qubits and a sample $z […]
Quantum 5, 559 (2021). https://doi.org/10.22331/q-2021-10-06-559 To explore the possibilities of a near-term intermediate-scale quantum algorithm and long-term fault-tolerant quantum computing, a fast and versatile quantum circuit simulator is needed. Here, we introduce Qulacs, a fast […]
Quantum 5, 558 (2021). https://doi.org/10.22331/q-2021-10-05-558 Barren plateau landscapes correspond to gradients that vanish exponentially in the number of qubits. Such landscapes have been demonstrated for variational quantum algorithms and quantum neural networks with either deep […]
Quantum 5, 557 (2021). https://doi.org/10.22331/q-2021-10-05-557 Gate set tomography (GST) is a protocol for detailed, predictive characterization of logic operations (gates) on quantum computing processors. Early versions of GST emerged around 2012-13, and since then it […]
Quantum 5, 556 (2021). https://doi.org/10.22331/q-2021-09-29-556 We present a novel mapping for studying 2D many-body quantum systems by solving an effective, one-dimensional long-range model in place of the original two-dimensional short-range one. In particular, we address […]
Quantum 5, 555 (2021). https://doi.org/10.22331/q-2021-09-28-555 In a quantum measurement process, classical information about the measured system spreads throughout the environment. Meanwhile, quantum information about the system becomes inaccessible to local observers. Here we prove a […]
Quantum 5, 554 (2021). https://doi.org/10.22331/q-2021-09-28-554 We consider a model of quantum computation using qubits where it is possible to measure whether a given pair are in a singlet (total spin $0$) or triplet (total spin […]
Quantum 5, 553 (2021). https://doi.org/10.22331/q-2021-09-28-553 Topological protection is employed in fault-tolerant error correction and in developing quantum algorithms with topological qubits. But, topological protection $textit{intrinsic to models being simulated}$, also robustly protects calculations, even on […]
Quantum 5, 552 (2021). https://doi.org/10.22331/q-2021-09-28-552 Given a Bell inequality, if its maximal quantum violation can be achieved only by a single set of measurements for each party or a single quantum state, up to local […]
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