Search results for "quantum computer"
showing 10 items of 211 documents
Magic informationally complete POVMs with permutations
2017
Eigenstates of permutation gates are either stabilizer states (for gates in the Pauli group) or magic states, thus allowing universal quantum computation [M. Planat and Rukhsan-Ul-Haq, Preprint 1701.06443]. We show in this paper that a subset of such magic states, when acting on the generalized Pauli group, define (asymmetric) informationally complete POVMs. Such IC-POVMs, investigated in dimensions $2$ to $12$, exhibit simple finite geometries in their projector products and, for dimensions $4$ and $8$ and $9$, relate to two-qubit, three-qubit and two-qutrit contextuality.
Span programs for functions with constant-sized 1-certificates
2012
Besides the Hidden Subgroup Problem, the second large class of quantum speed-ups is for functions with constant-sized 1-certificates. This includes the OR function, solvable by the Grover algorithm, the element distinctness, the triangle and other problems. The usual way to solve them is by quantum walk on the Johnson graph. We propose a solution for the same problems using span programs. The span program is a computational model equivalent to the quantum query algorithm in its strength, and yet very different in its outfit. We prove the power of our approach by designing a quantum algorithm for the triangle problem with query complexity O(n35/27) that is better than O(n13/10) of the best p…
Adiabatic creation of entangled states by a bichromatic field designed from the topology of the dressed eigenenergies
2002
Preparation of entangled pairs of coupled two-state systems driven by a bichromatic external field is studied. We use a system of two coupled spin-1/2 that can be translated into a three-state ladder model whose intermediate state represents the entangled state. We show that this entangled state can be prepared in a robust way with appropriate fields. Their frequencies and envelopes are derived from the topological properties of the model.
Experimental Engineering of Arbitrary Qudit States with Discrete-Time Quantum Walks
2019
The capability to generate and manipulate quantum states in high-dimensional Hilbert spaces is a crucial step for the development of quantum technologies, from quantum communication to quantum computation. One-dimensional quantum walk dynamics represents a valid tool in the task of engineering arbitrary quantum states. Here we affirm such potential in a linear-optics platform that realizes discrete-time quantum walks in the orbital angular momentum degree of freedom of photons. Different classes of relevant qudit states in a six-dimensional space are prepared and measured, confirming the feasibility of the protocol. Our results represent a further investigation of quantum walk dynamics in p…
Measurement-induced optical Kerr interaction
2013
We present a method for implementing a weak optical Kerr interaction (single-mode Kerr Hamiltonian) in a measurement-based fashion using the common set of universal elementary interactions for continuous-variable quantum computation. Our scheme is a conceptually distinct alternative to the use of naturally occurring, weak Kerr nonlinearities or specially designed nonlinear media. Instead, we propose to exploit suitable offline prepared quartic ancilla states together with beam splitters, squeezers, and homodyne detectors. For perfect ancilla states and ideal operations, our decompositions for obtaining the measurement-based Kerr Hamiltonian lead to a realization with near-unit fidelity. Non…
High-dimensional one-way quantum processing implemented on d-level cluster states
2019
Taking advantage of quantum mechanics for executing computational tasks faster than classical computers1 or performing measurements with precision exceeding the classical limit2,3 requires the generation of specific large and complex quantum states. In this context, cluster states4 are particularly interesting because they can enable the realization of universal quantum computers by means of a ‘one-way’ scheme5, where processing is performed through measurements6. The generation of cluster states based on sub-systems that have more than two dimensions, d-level cluster states, provides increased quantum resources while keeping the number of parties constant7, and also enables novel algorithm…
Driven Appearance and Disappearance of Quantum Zeno Effect in the Dynamics of a Four-level Trapped Ion
2001
An example of constrained unitary quantum dynamics in the context of trapped ions is given. We study a laser driven four-level ion system confined in an isotropic three-dimensional Paul microtrap. Our main result is that when two independent controllable continuous measurement processes are simultaneously present, the unitary quantum dynamics of the system can be parametrically frozen into a one-dimensional Hilbert subspace (Quantum Zeno Effect) or constrained into a two-dimensional one, at will. Conditions under which one of the two processes acts upon the physical system inhibiting the effects due to the other one, are explicitly found and discussed (Hierarchically Controlled Dynamics).
Co(II) chemistry of 2,6-bis(2-pyridylcarbonyl)pyridine: an icosanuclear Co cluster exhibiting superparamagnetic relaxation.
2006
High-nuclearity transition-metal complexes (clusters) are of special interest in chemistry and physics because, both in terms of size and physical properties, they bridge the gap between the microscopic and macroscopic world, and between quantum and classical systems. In terms of size, the smallest classical nanoparticles fabricated today are the same size as the largest metal clusters that are synthesized by bottom-up methods. In terms of physical properties, certain transition-metal clusters exhibit single-molecule magnetism at low temperatures, that is, they retain their magnetization in zero field in a manner analogous to that of classical macroscopic magnets, but at the same time they …
Rovibrational controlled-NOT gates using optimized stimulated Raman adiabatic passage techniques and optimal control theory
2009
Implementation of quantum controlled-NOT (CNOT) gates in realistic molecular systems is studied using stimulated Raman adiabatic passage (STIRAP) techniques optimized in the time domain by genetic algorithms or coupled with optimal control theory. In the first case, with an adiabatic solution (a series of STIRAP processes) as starting point, we optimize in the time domain different parameters of the pulses to obtain a high fidelity in two realistic cases under consideration. A two-qubit CNOT gate constructed from different assignments in rovibrational states is considered in diatomic (NaCs) or polyatomic $({\text{SCCl}}_{2})$ molecules. The difficulty of encoding logical states in pure rota…
Reversible solvatomagnetic switching in a single-ion magnet from an entatic state
2016
We have developed a new strategy for the design and synthesis of multifunctional molecular materials showing reversible magnetic and optical switching.