Quantum state tomography, the ability to deduce the density matrix of a quantum system from measu... more Quantum state tomography, the ability to deduce the density matrix of a quantum system from measured data, is of fundamental importance for the verification of present and future quantum devices. It has been realized in systems with few components but for larger systems it becomes rapidly infeasible because the number of quantum measurements and computational resources required to process them
We propose a driven optical cavity quantum electrodynamics (QED) set up aimed at directly probing... more We propose a driven optical cavity quantum electrodynamics (QED) set up aimed at directly probing energy transport dynamics in photosynthetic biomolecules. We show that detailed information concerning energy transfer paths and delocalization of exciton states can be inferred (and exciton energies estimated) from the statistical properties of the emitted photons. This approach provides us with a novel spectroscopic tool for
Natural and artificial light-harvesting processes have recently gained new interest. Signatures o... more Natural and artificial light-harvesting processes have recently gained new interest. Signatures of long-lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization-controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence.
Entanglement manipulation, and especially Entanglement Swapping is at the heart of current work o... more Entanglement manipulation, and especially Entanglement Swapping is at the heart of current work on quantum information processing, purification and quantum teleportation. We will discuss how it may be generalized to multiparticle systems and how this enables multi-user quantum cryptographic protocols to be developed. Our scheme allows us to establish multiparticle entanglement between particles which belong to distant users in a
ABSTRACT We apply quantum control techniques to a long spin chain by acting only on two qubits at... more ABSTRACT We apply quantum control techniques to a long spin chain by acting only on two qubits at one of its ends, thereby implementing universal quantum computation by a combination of quantum gates on these qubits and indirect SWAP operations across the chain. It is shown that the control sequences can be computed and implemented efficiently. We discuss the application of these ideas to physical systems such as superconducting qubits in which full control of long chains is challenging.
We present an analytical formula for the asymptotic relative entropy of entanglement with respect... more We present an analytical formula for the asymptotic relative entropy of entanglement with respect to positive partial transpose states for Werner states of arbitrary dimension. We then demonstrate its validity using methods from convex optimization. This is the first case in which the asymptotic value of a subadditive entanglement measure has been calculated.
... The goal will be to use these energy shifts to create a conditional dynamics of the two qubit... more ... The goal will be to use these energy shifts to create a conditional dynamics of the two qubits. ... In summary, we have demonstrated that a system con-sisting of ions trapped inside of a far detuned optical cavity can be used to implement coherent quantum in-formation ...
This article discusses the concept of information and its intimate relationship with physics. Aft... more This article discusses the concept of information and its intimate relationship with physics. After an introduction of all the necessary quantum mechanical and information theoretical concepts we analyse Landauer's principle which states that the erasure of information is inevitably accompanied by the generation of heat. We employ this principle to rederive a number of results in classical and quantum information theory whose rigorous mathematical derivations are difficult. This demonstrates the usefulness of Landauer's principle and provides an introduction to the physical theory of information.
We investigate the entanglement between two separated segments in the vacuum state of a free 1D K... more We investigate the entanglement between two separated segments in the vacuum state of a free 1D Klein-Gordon field, where explicit computations are performed in the continuum limit of the linear harmonic chain. We show that the entanglement, which we measure by the logarithmic negativity, is finite with no further need for renormalization. We find that the quantum correlations decay much
Demonstrating the subtraction of a single photon from one mode of a two-mode squeezed state repre... more Demonstrating the subtraction of a single photon from one mode of a two-mode squeezed state represents a significant step in the realization of continuous-variable quantum repeater protocols [1, 2]. Photon subtraction is a non-Gaussian operation, taking Gaussian phase-space quasi-probability distributions (such as Wigner functions) to non-Gaussian phase-space distributions, and can increase entanglement [3]. Non-Gaussian operations are neccesary for continuousvariable entanglement distillation [2, 4]. Entanglement increase has been demonstrated by using a ...
2008 Quantum Electronics and Laser Science Conference (QELS), 2008
A quantum protocol or experiment can be divided into three stages: preparation, processing, and m... more A quantum protocol or experiment can be divided into three stages: preparation, processing, and measurement. Quantum state [1, 2, 3] and process tomography [4, 5] respectively prescribe a procedure to completely characterise the first two stages and have been successfully shown experimentally. We complete this triad by implementing a method to determine the set of POVMs for an arbitrary quantum detector [6]. Thus without any knowledge of the inner workings of the detector we can predict its response to any input. Precise knowledge of the detector ...
2009 Conference on Lasers & Electro Optics & The Pacific Rim Conference on Lasers and Electro-Optics (CLEO/PACIFIC RIM), 2009
HB Coldenstrodt-Ronge1, AP Worsley1, JS Lundeen1,2, A. Feito3,4, KL Pregnell3,4, Ch. Silberhorn5,... more HB Coldenstrodt-Ronge1, AP Worsley1, JS Lundeen1,2, A. Feito3,4, KL Pregnell3,4, Ch. Silberhorn5, PJ Mosley1,5, BJ Smith1, G. Puentes1, N. Thomas-Peter1, TC Ralph6, J. Eisert3,4, MB Plenio3,4 and IA Walmsley1 ... 1Clarendon Laboratory, University of Oxford, Oxford, 0X1 3PU, UK 2Institute for National Measurement Standards, Ottawa, ON, Canada K1A 0R6 3Institute for Mathematical Sciences, Imperial College London, SW7 2PE, UK 4QOLS, The Blackett Laboratory, Imperial College London, Prince Consort Rd., SW7 2BW, UK 5Max- ...
Quantum state tomography, the ability to deduce the density matrix of a quantum system from measu... more Quantum state tomography, the ability to deduce the density matrix of a quantum system from measured data, is of fundamental importance for the verification of present and future quantum devices. It has been realized in systems with few components but for larger systems it becomes rapidly infeasible because the number of quantum measurements and computational resources required to process them
We propose a driven optical cavity quantum electrodynamics (QED) set up aimed at directly probing... more We propose a driven optical cavity quantum electrodynamics (QED) set up aimed at directly probing energy transport dynamics in photosynthetic biomolecules. We show that detailed information concerning energy transfer paths and delocalization of exciton states can be inferred (and exciton energies estimated) from the statistical properties of the emitted photons. This approach provides us with a novel spectroscopic tool for
Natural and artificial light-harvesting processes have recently gained new interest. Signatures o... more Natural and artificial light-harvesting processes have recently gained new interest. Signatures of long-lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization-controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence.
Entanglement manipulation, and especially Entanglement Swapping is at the heart of current work o... more Entanglement manipulation, and especially Entanglement Swapping is at the heart of current work on quantum information processing, purification and quantum teleportation. We will discuss how it may be generalized to multiparticle systems and how this enables multi-user quantum cryptographic protocols to be developed. Our scheme allows us to establish multiparticle entanglement between particles which belong to distant users in a
ABSTRACT We apply quantum control techniques to a long spin chain by acting only on two qubits at... more ABSTRACT We apply quantum control techniques to a long spin chain by acting only on two qubits at one of its ends, thereby implementing universal quantum computation by a combination of quantum gates on these qubits and indirect SWAP operations across the chain. It is shown that the control sequences can be computed and implemented efficiently. We discuss the application of these ideas to physical systems such as superconducting qubits in which full control of long chains is challenging.
We present an analytical formula for the asymptotic relative entropy of entanglement with respect... more We present an analytical formula for the asymptotic relative entropy of entanglement with respect to positive partial transpose states for Werner states of arbitrary dimension. We then demonstrate its validity using methods from convex optimization. This is the first case in which the asymptotic value of a subadditive entanglement measure has been calculated.
... The goal will be to use these energy shifts to create a conditional dynamics of the two qubit... more ... The goal will be to use these energy shifts to create a conditional dynamics of the two qubits. ... In summary, we have demonstrated that a system con-sisting of ions trapped inside of a far detuned optical cavity can be used to implement coherent quantum in-formation ...
This article discusses the concept of information and its intimate relationship with physics. Aft... more This article discusses the concept of information and its intimate relationship with physics. After an introduction of all the necessary quantum mechanical and information theoretical concepts we analyse Landauer's principle which states that the erasure of information is inevitably accompanied by the generation of heat. We employ this principle to rederive a number of results in classical and quantum information theory whose rigorous mathematical derivations are difficult. This demonstrates the usefulness of Landauer's principle and provides an introduction to the physical theory of information.
We investigate the entanglement between two separated segments in the vacuum state of a free 1D K... more We investigate the entanglement between two separated segments in the vacuum state of a free 1D Klein-Gordon field, where explicit computations are performed in the continuum limit of the linear harmonic chain. We show that the entanglement, which we measure by the logarithmic negativity, is finite with no further need for renormalization. We find that the quantum correlations decay much
Demonstrating the subtraction of a single photon from one mode of a two-mode squeezed state repre... more Demonstrating the subtraction of a single photon from one mode of a two-mode squeezed state represents a significant step in the realization of continuous-variable quantum repeater protocols [1, 2]. Photon subtraction is a non-Gaussian operation, taking Gaussian phase-space quasi-probability distributions (such as Wigner functions) to non-Gaussian phase-space distributions, and can increase entanglement [3]. Non-Gaussian operations are neccesary for continuousvariable entanglement distillation [2, 4]. Entanglement increase has been demonstrated by using a ...
2008 Quantum Electronics and Laser Science Conference (QELS), 2008
A quantum protocol or experiment can be divided into three stages: preparation, processing, and m... more A quantum protocol or experiment can be divided into three stages: preparation, processing, and measurement. Quantum state [1, 2, 3] and process tomography [4, 5] respectively prescribe a procedure to completely characterise the first two stages and have been successfully shown experimentally. We complete this triad by implementing a method to determine the set of POVMs for an arbitrary quantum detector [6]. Thus without any knowledge of the inner workings of the detector we can predict its response to any input. Precise knowledge of the detector ...
2009 Conference on Lasers & Electro Optics & The Pacific Rim Conference on Lasers and Electro-Optics (CLEO/PACIFIC RIM), 2009
HB Coldenstrodt-Ronge1, AP Worsley1, JS Lundeen1,2, A. Feito3,4, KL Pregnell3,4, Ch. Silberhorn5,... more HB Coldenstrodt-Ronge1, AP Worsley1, JS Lundeen1,2, A. Feito3,4, KL Pregnell3,4, Ch. Silberhorn5, PJ Mosley1,5, BJ Smith1, G. Puentes1, N. Thomas-Peter1, TC Ralph6, J. Eisert3,4, MB Plenio3,4 and IA Walmsley1 ... 1Clarendon Laboratory, University of Oxford, Oxford, 0X1 3PU, UK 2Institute for National Measurement Standards, Ottawa, ON, Canada K1A 0R6 3Institute for Mathematical Sciences, Imperial College London, SW7 2PE, UK 4QOLS, The Blackett Laboratory, Imperial College London, Prince Consort Rd., SW7 2BW, UK 5Max- ...
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