Spectral implementation of some quantum algorithms by one- and two-dimensional nuclear magnetic resonance

Quantum information processing has been effectively demonstrated on a small number of qubits by nuclear magnetic resonance. An important subroutine in any computing is the readout of the output. ``Spectral implementation'' originally suggested by Z.L. Madi, R. Bruschweiler and R.R. Ernst, [J. Chem. Phys. 109, 10603 (1999)], provides an elegant method of readout with the use of an extra `observer' qubit. At the end of computation, detection of the observer qubit provides the output via the multiplet structure of its spectrum. In "spectral implementation" by two-dimensional experiment the observer qubit retains the memory of input state during computation, thereby providing correlated information on input and output, in the same spectrum. "Spectral implementation" of Grover's search algorithm, approximate quantum counting, a modified version of Berstein-Vazirani problem, and Hogg's algorithm is demonstrated here in three and four-qubit systems.Comment: 39 pages,11 figure

Efficient, low noise, mode-selective quantum memory

Photonic quantum information processing is a key element for scalable quantum technologies, and has applications in secure long-distance quantum communication and connecting nodes of a quantum computation network. However, logical photon-photon gates and state-of-the-art single photon sources rely on probabilistic processes. Quantum memories are devices that enable storage and on-demand recall of quantum states of light, and have been highlighted as a vital component in photonic networks to overcome the scaling problem by synchronising probabilistic processes. The Raman memory has a large storage bandwidth and high synchronising capacity, and is an ideal candidate for local synchronisation. However, previous demonstrations of the Raman memory suffer from four-wave mixing noise, which prohibits quantum level operation. In this thesis I investigate methods to increase the signal to noise ratio in the Raman memory. I investigate increasing the light-matter coupling strength to boost the memory efficiency, and then explore two different methods to suppress four-wave mixing noise. I demonstrate that operating the Raman memory in a cavity is successful in reducing four-wave mixing, but it is technically challenging to maintain a high memory efficiency. I investigate a new method of noise suppression by introducing an absorption feature at the frequency of the unwanted noise field. This technically simple method is successful in reducing the noise by an order of magnitude, and will be applicable to many quantum memory protocols. In the final section of this thesis I explore the temporal mode properties of the Raman memory. I demonstrate that the Raman memory is single mode and can be used to separate and manipulate temporal modes of light. This positions the Raman memory as a key device for enabling high-dimensional photonic quantum information processing, and enhancing light-matter interactions. These results pave the way towards an efficient, low-noise, mode-selective quantum memory.Open Acces

Quantum manipulation of photons and atoms : the application in quantum information processing

Quantum information has been witnessing great science value and latent application since 1980's. The research work presented here consist of mainly two important parts: manipulations of multiphoton entanglement and atomic ensembles based quantum memory. In first part, the experimental technique multi-photon entanglement is further developed to study fundamental issues in quantum mechanics, remarkable applications to quantum communication and quantum computation. Specifically, we have demonstrated a bit-flip error-free transfer of quantum information, violation of Bell's inequality beyond Tsirelson's bound, teleportation of a two-qubit composite system, as well as the one-way computing by two-photon-four-qubit cluster state. To overcome un-scalability problem due to probabilistic feature in linear optical quantum information processing, we investigated in the second part the physics of atomic ensembles based quantum memory. We show that theoretically, entanglement between distant locations can be deterministically generated. The experimental work has thoroughly developed the necessary techniques and we have achieved deterministic single photon source, and interference of the photons from independent atomic ensembles, teleportation between photonic and atomic qubits, a novel way to create a robust entanglement between an atomic and a photonic qubit, and memory based entanglement swapping. We believe, the developed techniques here would dramatically facilitate progresses in many fields including global quantum communication, linear optical quantum computation and the foundations of quantum mechanics etc

Quantum-enhanced barcode decoding and pattern recognition

Quantum hypothesis testing is one of the most fundamental problems in quantum information theory, with crucial implications in areas like quantum sensing, where it has been used to prove quantum advantage in a series of binary photonic protocols, e.g., for target detection or memory cell readout. In this work, we generalize this theoretical model to the multi-partite setting of barcode decoding and pattern recognition. We start by defining a digital image as an array or grid of pixels, each pixel corresponding to an ensemble of quantum channels. Specializing each pixel to a black and white alphabet, we naturally define an optical model of barcode. In this scenario, we show that the use of quantum entangled sources, combined with suitable measurements and data processing, greatly outperforms classical coherent-state strategies for the tasks of barcode data decoding and classification of black and white patterns. Moreover, introducing relevant bounds, we show that the problem of pattern recognition is significantly simpler than barcode decoding, as long as the minimum Hamming distance between images from different classes is large enough. Finally, we theoretically demonstrate the advantage of using quantum sensors for pattern recognition with the nearest neighbor classifier, a supervised learning algorithm, and numerically verify this prediction for handwritten digit classification

Are dark photons behind biophotons?

TGD approach leads to a prediction that biophotons result when dark photons with large value of effective Planck constant and large wavelength transform to ordinary photons with same energy. The collaboration with Lian Sidorov stimulated a more detailed look for what biophotons are. Also the recent progress in understanding the implications of basic vision behind TGD inspired theory of consciousness erved as an additional motivation for a complementary treatment. 1. The anatomy of quantum jump in zero energy ontology (ZEO) allows to understand basic aspects of sensory and cognitive processing in brain without ever mentioning brain. Sensory perception - motor action cycle with motor action allowing interpretation as time reversed sensory perception reflects directly the fact that state function reductions occur alternately to the two opposite boundaries of causal diamond (which itself or rather, quantum superposition of CDs, changes in the process). 2. Also the abstraction and de-abstraction processes in various scales which are essential for the neural processing emerge already at the level of quantum jump. The formation of associations is one aspect of abstraction since it combines different manners to experience the same object. Negentropic entanglement of two or more mental images (CDs) gives rise to rules in which superposed n-particle states correspond to instances of the rule. Tensor product formation generating negentropic entanglement between new mental images and earlier ones generates longer sequences of memory mental images and gives rise to negentropy gain generating experience of understanding, recognition, something which has positive emotional coloring. Quantum superposition of perceptively equivalent zero energy states in given resolution gives rise to averaging. Increasing the abstraction level means poorer resolution so that the insignificant details are not perceived. 3. Various memory representations should be approximately invariant under the sequence of quantum jumps. Negentropic entanglement gives rise to this kind of stabilization. The assumption that self model is a negentropically entangled system which does not change in state function reduction, leads to a problem. If the conscious information about this kind of subself corresponds to change of negentropy in quantum jump, it seems impossible to get this information. Quite generally, if moment of consciousness corresponds to quantum jump and thus change, how it is possible to carry conscious information about quantum state? Interaction free measurement however allows to circumvent the problem: non-destructive reading of memories and future plans becomes possible in arbitrary good approximation. This memory reading mechanism can be formulated for both photons and photons and these two reading mechanisms could correspond to visual memories as imagination and auditory memories as internal speech. Therefore dark photons decaying to biophotons could be crucial element of imagination and the notion bio-phonon could also make sense and even follow as a prediction. This would also suggest a correlation of biophoton emission with EEG for which there is a considerable evidence. The observation that biophotons seem to be associated only with the right hemisphere suggests that at least some parts of right hemisphere prefer dark photons and are thus specialized to visual imagination: spatial relationships are the speciality of the right hemisphere. Some parts the of left hemisphere at least might prefer dark photons in IR energy range transforming to ordinary phonons in ear or dark phonons: left hemisphere is indeed the verbal hemisphere specialized to linear linguistic cognition. In the sequel I shall discuss biophotons in TGD Universe as decay products of dark photons and propose among other things an explanation for the hyperbolic decay law in terms of quantum coherence and echo like mechanism guaranteing replication of memory representations. Applications to biology, neuroscience, and consciousness are discussed and also the possible role of biophotons for remote mental interactions is considered. Also the phenomenon of taos hum is discussed as a possible evidence for biophonons

A Computational Model for Quantum Measurement

Is the dynamical evolution of physical systems objectively a manifestation of information processing by the universe? We find that an affirmative answer has important consequences for the measurement problem. In particular, we calculate the amount of quantum information processing involved in the evolution of physical systems, assuming a finite degree of fine-graining of Hilbert space. This assumption is shown to imply that there is a finite capacity to sustain the immense entanglement that measurement entails. When this capacity is overwhelmed, the system's unitary evolution becomes computationally unstable and the system suffers an information transition (`collapse'). Classical behaviour arises from the rapid cycles of unitary evolution and information transitions. Thus, the fine-graining of Hilbert space determines the location of the `Heisenberg cut', the mesoscopic threshold separating the microscopic, quantum system from the macroscopic, classical environment. The model can be viewed as a probablistic complement to decoherence, that completes the measurement process by turning decohered improper mixtures of states into proper mixtures. It is shown to provide a natural resolution to the measurement problem and the basis problem.Comment: 24 pages; REVTeX4; published versio

Can biological quantum networks solve NP-hard problems?

There is a widespread view that the human brain is so complex that it cannot be efficiently simulated by universal Turing machines. During the last decades the question has therefore been raised whether we need to consider quantum effects to explain the imagined cognitive power of a conscious mind. This paper presents a personal view of several fields of philosophy and computational neurobiology in an attempt to suggest a realistic picture of how the brain might work as a basis for perception, consciousness and cognition. The purpose is to be able to identify and evaluate instances where quantum effects might play a significant role in cognitive processes. Not surprisingly, the conclusion is that quantum-enhanced cognition and intelligence are very unlikely to be found in biological brains. Quantum effects may certainly influence the functionality of various components and signalling pathways at the molecular level in the brain network, like ion ports, synapses, sensors, and enzymes. This might evidently influence the functionality of some nodes and perhaps even the overall intelligence of the brain network, but hardly give it any dramatically enhanced functionality. So, the conclusion is that biological quantum networks can only approximately solve small instances of NP-hard problems. On the other hand, artificial intelligence and machine learning implemented in complex dynamical systems based on genuine quantum networks can certainly be expected to show enhanced performance and quantum advantage compared with classical networks. Nevertheless, even quantum networks can only be expected to efficiently solve NP-hard problems approximately. In the end it is a question of precision - Nature is approximate.Comment: 38 page