Quantum 5, 444 (2021). https://doi.org/10.22331/q-2021-04-26-444 Device-independent quantum key distribution aims at providing security guarantees even when using largely uncharacterised devices. In the simplest scenario, these guarantees are derived from the CHSH score, which is a […]
Quantum 5, 443 (2021). https://doi.org/10.22331/q-2021-04-26-443 The simplest device-independent quantum key distribution protocol is based on the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality and allows two users, Alice and Bob, to generate a secret key if they observe […]
Quantum 5, 442 (2021). https://doi.org/10.22331/q-2021-04-26-442 We analyse orthogonal bases in a composite $Ntimes N$ Hilbert space describing a bipartite quantum system and look for a basis with optimal single-sided mutual state distinguishability. This condition implies […]
Quantum 5, 441 (2021). https://doi.org/10.22331/q-2021-04-26-441 Similarly to quantum states, quantum operations can also be transformed by means of quantum superchannels, also known as process matrices. Quantum superchannels with multiple slots are deterministic transformations which take […]
Quantum 5, 440 (2021). https://doi.org/10.22331/q-2021-04-26-440 We present a method to detect quantum memory in a non-Markovian process. We call a process Markovian when the environment does not provide a memory that retains correlations across different […]
Quantum 5, 439 (2021). https://doi.org/10.22331/q-2021-04-26-439 The exchange of information between an open quantum system and its environment allows us to discriminate among different kinds of dynamics, in particular detecting memory effects to characterize non-Markovianity. Here, […]
Quantum 5, 438 (2021). https://doi.org/10.22331/q-2021-04-22-438 We introduce “fractalization”, a procedure by which spin models are extended to higher-dimensional “fractal” spin models. This allows us to interpret type-II fracton phases, fractal symmetry-protected topological phases, and more, […]
Quantum 5, 437 (2021). https://doi.org/10.22331/q-2021-04-20-437 The $p$-stage Quantum Approximate Optimization Algorithm (QAOA$_p$) is a promising approach for combinatorial optimization on noisy intermediate-scale quantum (NISQ) devices, but its theoretical behavior is not well understood beyond $p=1$. […]
Quantum 5, 436 (2021). https://doi.org/10.22331/q-2021-04-20-436 Suppose we want to implement a unitary $U$, for instance a circuit for some quantum algorithm. Suppose our actual implementation is a unitary $tilde{U}$, which we can only apply as […]
Quantum 5, 435 (2021). https://doi.org/10.22331/q-2021-04-20-435 We investigate the conditions under which an uncontrollable background processes may be harnessed by an agent to perform a task that would otherwise be impossible within their operational framework. This […]
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