Fast Quantum Search Algorithms in Protein Sequence Comparison - Quantum Biocomputing

Quantum search algorithms are considered in the context of protein sequence comparison in biocomputing. Given a sample protein sequence of length m (i.e m residues), the problem considered is to find an optimal match in a large database containing N residues. Initially, Grover's quantum search algorithm is applied to a simple illustrative case - namely where the database forms a complete set of states over the 2^m basis states of a m qubit register, and thus is known to contain the exact sequence of interest. This example demonstrates explicitly the typical O(sqrt{N}) speedup on the classical O(N) requirements. An algorithm is then presented for the (more realistic) case where the database may contain repeat sequences, and may not necessarily contain an exact match to the sample sequence. In terms of minimizing the Hamming distance between the sample sequence and the database subsequences the algorithm finds an optimal alignment, in O(sqrt{N}) steps, by employing an extension of Grover's algorithm, due to Boyer, Brassard, Hoyer and Tapp for the case when the number of matches is not a priori known.Comment: LaTeX, 5 page

Limits to clock synchronization induced by completely dephasing communication channels

Clock synchronization procedures are analyzed in the presence of imperfect communications. In this context we show that there are physical limitations which prevent one from synchronizing distant clocks when the intervening medium is completely dephasing, as in the case of a rapidly varying dispersive medium.Comment: 6 Pages. Revised version as published in PR

NMR quantum computation with indirectly coupled gates

An NMR realization of a two-qubit quantum gate which processes quantum information indirectly via couplings to a spectator qubit is presented in the context of the Deutsch-Jozsa algorithm. This enables a successful comprehensive NMR implementation of the Deutsch-Jozsa algorithm for functions with three argument bits and demonstrates a technique essential for multi-qubit quantum computation.Comment: 9 pages, 2 figures. 10 additional figures illustrating output spectr

Implementation of a Deutsch-like quantum algorithm utilizing entanglement at the two-qubit level, on an NMR quantum information processor

We describe the experimental implementation of a recently proposed quantum algorithm involving quantum entanglement at the level of two qubits using NMR. The algorithm solves a generalisation of the Deutsch problem and distinguishes between even and odd functions using fewer function calls than is possible classically. The manipulation of entangled states of the two qubits is essential here, unlike the Deutsch-Jozsa algorithm and the Grover's search algorithm for two bits.Comment: 4 pages, two eps figure

Solid-State Nuclear Spin Quantum Computer Based on Magnetic Resonance Force Microscopy

We propose a nuclear spin quantum computer based on magnetic resonance force microscopy (MRFM). It is shown that an MRFM single-electron spin measurement provides three essential requirements for quantum computation in solids: (a) preparation of the ground state, (b) one- and two- qubit quantum logic gates, and (c) a measurement of the final state. The proposed quantum computer can operate at temperatures up to 1K.Comment: 16 pages, 5 figure

Measuring and modelling the impact of outdoor pigs on soil carbon and nutrient dynamics under a changing climate and different management scenarios

A mixed agricultural system that integrates livestock and cropping is essential to organic, agroecological, and regenerative farming. The demand for improved welfare systems has made the practice of outdoor rearing of pigs very popular; it currently makes up 40% of the UK pig industry and has also been integrated into arable rotations. Besides the benefits of outdoor production systems, they also potentially pose environmental risks to farmlands, such as accumulation of nitrogen and phosphorus in the soil, soil erosion and compaction and carbon loss. Despite this, the impact of outdoor pigs and arable crop rotations on soil health has been under-researched relative to other livestock species. This study was conducted at the University of Leeds Research Farm from 2018 to 2020 using a combined experimental and modelling approach to understand the impact of outdoor pigs on soil carbon and nutrient dynamics. The physio-chemical properties of arable soil were measured prior to the introduction of the pigs and after introducing the pigs at the end of first and second years, consecutively. There was assessment of control sites (without pigs, mowing once a year) and pig pens (pigs in a rotation with arable crops). The soil was sampled at two different depths, 0–10 cm and 10–20 cm. It was observed that measured soil organic carbon (SOC) stocks in the soil depths of 0–10 cm and 10–20 cm layer were decreased by 7% and 3%, respectively, in the pig pens from 2019 to 2020, and total available nitrogen and phosphorus were significantly higher in pig pens than the control sites. Hence, at a depth between 0 and 20 cm, the average total available nitrogen was 2.51 and 2.68 mg kg−1 in the control sites and 21.76 and 20.45 mg kg−1 in the pig pens in 2019 and 2020, respectively. The average total available phosphorus at 0–20 cm was 26.54 and 37.02 mg kg−1 in control sites and 48.15 and 63.58 mg kg−1 in pig pens during 2019 and 2020, respectively. A process-based model (DayCent) was used to simulate soil carbon and nitrogen dynamics in the arable rotation with outdoor pigs and showed SOC stock losses of – 0.09 ± 0.23 T C ha−1 year−1 using the future climate CMIP5 RCP 8.5 scenario for 2020 to 2048. To reduce this loss, we modelled the impact of changing the management of the pig rotation and found that the loss of SOC stock could be decreased by shortening the period of pig retention in the field, growing grass in the field, and leguminous crops in the crop rotation

Grover search with pairs of trapped ions

The desired interference required for quantum computing may be modified by the wave function oscillations for the implementation of quantum algorithms[Phys.Rev.Lett.84(2000)1615]. To diminish such detrimental effect, we propose a scheme with trapped ion-pairs being qubits and apply the scheme to the Grover search. It can be found that our scheme can not only carry out a full Grover search, but also meet the requirement for the scalable hot-ion quantum computing. Moreover, the ion-pair qubits in our scheme are more robust against the decoherence and the dissipation caused by the environment than single-particle qubits proposed before.Comment: RevTe

Single and double qubit gates by manipulating degeneracy

A novel mechanism is proposed for single and double qubit state manipulations in quantum computation with four-fold degenerate energy levels. The principle is based on starting with a four fold degeneracy, lifting it stepwise adiabatically by a set of control parameters and performing the quantum gate operations on non-degenerate states. A particular realization of the proposed mechanism is suggested by using inductively coupled rf-squid loops in the macroscopic quantum tunnelling regime where the energy eigen levels are directly connected with the measurable flux states. The one qubit and two qubit controlled operations are demonstrated explicitly. The appearance of the flux states also allows precise read-in and read-out operations by the measurement of flux.Comment: 6 pages + 5 figures (separately included

Toward scalable quantum computation with cavity QED systems

We propose a scheme for quantum computing using high-Q cavities in which the qubits are represented by single cavity modes restricted in the space spanned by the two lowest Fock states. We show that single qubit operations and universal multiple qubit gates can be implemented using atoms sequentially crossing the cavities.Comment: 14 pages, 8 figure

Selective quantum evolution of a qubit state due to continuous measurement

We consider a two-level quantum system (qubit) which is continuously measured by a detector. The information provided by the detector is taken into account to describe the evolution during a particular realization of measurement process. We discuss the Bayesian formalism for such ``selective'' evolution of an individual qubit and apply it to several solid-state setups. In particular, we show how to suppress the qubit decoherence using continuous measurement and the feedback loop.Comment: 15 pages (including 9 figures