Ground-state entanglement of spin-1 bosons undergoing superexchange interactions in optical superlattices

We discuss a model with ultra-cold atoms confined in optical superlattices. In particular, we study the ground-state properties of two spin-1 bosons trapped in a double-well potential. Depending on the external magnetic field and biquadratic interactions different phases of magnetic order are realized. Applying von Neumann entropy and number of relevant orbitals, we quantify the bipartite entanglement between particles. Changing the values of the parameters determining superlattices, we can switch the system between differently entangled states

Enhancement of non-Stabilizerness within Indefinite Causal Order

In the field of quantum computation, the non-stabilizerness of a quantum circuit is crucial for understanding and quantifying quantum speed-up. In this work, we explore some intriguing phenomena regarding the non-stabilizerness of a circuit when a Quantum SWITCH structure is employed. This structure is a novel quantum construct that enables quantum states to pass through operations in a superposition of different orders and has shown superiority in numerous tasks over circuits with a definite causal order. Firstly, we discover that the completely stabilizer-preserving operations, which cannot generate magic states under standard conditions, can be transformed into a resourceful operation capable of generating magic states when processed by the Quantum SWITCH. Secondly, when considering the effects of noisy channels on operations, we observe that while the non-stabilizerness of each path may be annihilated, their superposition could still preserve the non-stabilizerness of the operation. These findings reveal unique properties brought by the Quantum SWITCH and open further avenues in future research on magic resources of general quantum architecture.Comment: 5+4 pages, 4 figure

On the robustness of bucket brigade quantum RAM

We study the robustness of the bucket brigade quantum random access memory model introduced by Giovannetti, Lloyd, and Maccone [Phys. Rev. Lett. 100, 160501 (2008)]. Due to a result of Regev and Schiff [ICALP '08 pp. 773], we show that for a class of error models the error rate per gate in the bucket brigade quantum memory has to be of order $o(2^{-n/2})$ (where $N=2^n$ is the size of the memory) whenever the memory is used as an oracle for the quantum searching problem. We conjecture that this is the case for any realistic error model that will be encountered in practice, and that for algorithms with super-polynomially many oracle queries the error rate must be super-polynomially small, which further motivates the need for quantum error correction. By contrast, for algorithms such as matrix inversion [Phys. Rev. Lett. 103, 150502 (2009)] or quantum machine learning [Phys. Rev. Lett. 113, 130503 (2014)] that only require a polynomial number of queries, the error rate only needs to be polynomially small and quantum error correction may not be required. We introduce a circuit model for the quantum bucket brigade architecture and argue that quantum error correction for the circuit causes the quantum bucket brigade architecture to lose its primary advantage of a small number of "active" gates, since all components have to be actively error corrected.Comment: Replaced with the published version. 13 pages, 9 figure

Atomic quantum state transferring and swapping via quantum Zeno dynamics

In this paper, we first demonstrate how to realize quantum state transferring (QST) from one atom to another based on quantum Zeno dynamics. Then, the QST protocol is generalized to realize the quantum state swapping (QSS) between two arbitrary atoms with the help of a third one. Furthermore, we also consider the QSS within a quantum network. The influence of decoherence is analyzed by numerical calculation. The results demonstrate that the protocols are robust against cavity decay.Comment: To appear in J. Opt. Soc. Am. B (JOSAB