78
78

Sep 18, 2013
09/13

by
Daniel Burgarth

texts

#
eye 78

#
favorite 0

#
comment 0

The thesis covers various aspects of quantum state transfer in permanently coupled spin systems.

Source: http://arxiv.org/abs/0704.1309v1

78
78

Sep 21, 2013
09/13

by
Daniel Burgarth

texts

#
eye 78

#
favorite 0

#
comment 0

One of the most basic tasks required for Quantum Information Technology is the ability to connect different components of a Quantum Computer by quantum wires that obey the superposition principle. Since superpositions can be very sensitive to noise this turns out to be already quite difficult. Recently, it was suggested to use chains of permanently coupled spin-1/2 particles (quantum chains) for this purpose. They have the advantage that no external control along the wire is required during the...

Source: http://arxiv.org/abs/0706.0387v3

99
99

Sep 23, 2013
09/13

by
Daniel Burgarth; Koji Maruyama

texts

#
eye 99

#
favorite 0

#
comment 0

Identifying the nature of interactions in a quantum system is essential in understanding any physical phenomena. Acquiring information on the Hamiltonian can be a tough challenge in many-body systems because it generally requires access to all parts of the system. We show that if the coupling topology is known, the Hamiltonian identification is indeed possible indirectly even though only a small gateway to the system is used. Surprisingly, even a degenerate Hamiltonian can be estimated by...

Source: http://arxiv.org/abs/0903.0612v1

63
63

Sep 20, 2013
09/13

by
Daniel Burgarth; Sougato Bose

texts

#
eye 63

#
favorite 0

#
comment 0

We investigate the effect of a spin bath on the spin transfer functions of a permanently coupled spin system. When each spin is coupled to a seperate environment, the effect on the transfer functions in the first excitation sector is amazingly simple: the group velocity is slowed down by a factor of two, and the fidelity is destabilized by a modulation of |cos Gt|, where G is the mean square coupling to the environment.

Source: http://arxiv.org/abs/quant-ph/0601047v2

104
104

Sep 18, 2013
09/13

by
Daniel Burgarth; Vittorio Giovannetti

texts

#
eye 104

#
favorite 0

#
comment 0

We give a simple and physically intuitive necessary and sufficient condition for a map acting on a compact metric space to be mixing (i.e. infinitely many applications of the map transfer any input into a fixed convergency point). This is a generalization of the "Lyapunov direct method". First we prove this theorem in topological spaces and for arbitrary continuous maps. Finally we apply our theorem to maps which are relevant in Open Quantum Systems and Quantum Information, namely...

Source: http://arxiv.org/abs/quant-ph/0605197v3

62
62

Sep 23, 2013
09/13

by
Daniel Burgarth; Vittorio Giovannetti

texts

#
eye 62

#
favorite 0

#
comment 0

In this addendum of our paper [D. Burgarth and V. Giovannetti, Phys. Rev. Lett. 99, 100501 (2007)] we prove that during the transformation that allows one to enforce control by relaxation on a quantum system, the ancillary memory can be kept at a finite size, independently from the fidelity one wants to achieve. The result is obtained by introducing the quantum analog of defragmentation algorithms which are employed for efficiently reorganizing classical information in conventional hard-disks....

Source: http://arxiv.org/abs/1006.4107v1

63
63

Sep 21, 2013
09/13

by
Daniel Burgarth; Kazuya Yuasa

texts

#
eye 63

#
favorite 0

#
comment 0

The aim of quantum system identification is to estimate the ingredients inside a black box, in which some quantum-mechanical unitary process takes place, by just looking at its input-output behavior. Here we establish a basic and general framework for quantum system identification, that allows us to classify how much knowledge about the quantum system is attainable, in principle, from a given experimental setup. Prior knowledge on some elements of the black box helps the system identification....

Source: http://arxiv.org/abs/1104.0583v1

6
6.0

Jun 30, 2018
06/18

by
Koji Maruyama; Daniel Burgarth

texts

#
eye 6

#
favorite 0

#
comment 0

Towards the full-fledged quantum computing, what do we need? Obviously, the first thing we need is a (many-body) quantum system, which is reasonably isolated from its environment in order to reduce the unwanted effect of noise, and the second might be a good technique to fully control it. Although we would also need a well-designed quantum code for information processing for fault-tolerant computation, from a physical point of view, the primary requisites are a system and a full control for it....

Topic: Quantum Physics

Source: http://arxiv.org/abs/1701.00216

43
43

Sep 19, 2013
09/13

by
Daniel Burgarth; Vittorio Giovannetti

texts

#
eye 43

#
favorite 0

#
comment 0

Homogenization protocols model the quantum mechanical evolution of a system to a fixed state independently from its initial configuration by repeatedly coupling it with a collection of identical ancillas. Here we analyze these protocols within the formalism of "relaxing" channels providing an easy to check sufficient condition for homogenization. In this context we describe mediated homogenization schemes where a network of connected qudits relaxes to a fixed state by only partially...

Source: http://arxiv.org/abs/0708.2657v2

8
8.0

Jun 28, 2018
06/18

by
Jukka Kiukas; Daniel Burgarth

texts

#
eye 8

#
favorite 0

#
comment 0

We demonstrate how quantum optimal control can be used to enhance quantum resources for bipartite one-way protocols, specifically EPR-steering with qubit measurements. Steering is relevant for one-sided device-independent key distribution, the realistic implementations of which necessitate the study of noisy scenarios. So far mainly the case of imperfect detection efficiency has been considered; here we look at the effect of dynamical noise responsible for decoherence and dissipation. In order...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.08822

83
83

Sep 23, 2013
09/13

by
Daniel Burgarth; Vittorio Giovannetti

texts

#
eye 83

#
favorite 0

#
comment 0

We discuss an explicit protocol which allows one to externally cool and control a composite system by operating on a small subset of it. The scheme permits to transfer arbitrary and unknown quantum states from a memory on the network ("upload access") as well as the inverse ("download access"). In particular it yields a method for cooling the system.

Source: http://arxiv.org/abs/0710.0302v4

45
45

Sep 18, 2013
09/13

by
Daniel Burgarth; Vittorio Giovannetti

texts

#
eye 45

#
favorite 0

#
comment 0

We demonstrate a scheme for controlling a large quantum system by acting on a small subsystem only. The local control is mediated to the larger system by some fixed coupling Hamiltonian. The scheme allows to transfer arbitrary and unknown quantum states from a memory on the large system (``upload access'') as well as the inverse (``download access''). We study sufficient conditions of the coupling Hamiltonian and give lower bounds on the fidelities for downloading and uploading.

Source: http://arxiv.org/abs/0704.3027v1

4
4.0

Jun 30, 2018
06/18

by
Daniel Burgarth; Kazuya Yuasa

texts

#
eye 4

#
favorite 0

#
comment 0

We provide a general framework for the identification of open quantum systems. By looking at the input-output behavior, we try to identify the system inside a black box in which some Markovian time-evolution takes place. Due to the generally irreversible nature of the dynamics, it is difficult to assure full controllability over the system. Still, we show that the system is identifiable up to similarity under a certain rank condition. The framework also covers situations relevant to standard...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1401.5240

45
45

Sep 21, 2013
09/13

by
Vittorio Giovannetti; Daniel Burgarth

texts

#
eye 45

#
favorite 0

#
comment 0

We demonstrate that the quantum communication between two parties can be significantly improved if the receiver is allowed to store the received signals in a quantum memory before decoding them. In the limit of an infinite memory, the transfer is perfect. We prove that this scheme allows the transfer of arbitrary multipartite states along Heisenberg chains of spin-1/2 particles with random coupling strengths.

Source: http://arxiv.org/abs/quant-ph/0508022v2

44
44

Sep 18, 2013
09/13

by
Daniel Burgarth; Sougato Bose

texts

#
eye 44

#
favorite 0

#
comment 0

We suggest a scheme that allows arbitrarily perfect state transfer even in the presence of random fluctuations in the couplings of a quantum chain. The scheme performs well for both spatially correlated and uncorrelated fluctuations if they are relatively weak (say 5%). Furthermore, we show that given a quite arbitrary pair of quantum chains, one can check whether it is capable of perfect transfer by only local operations at the ends of the chains, and the system in the middle being a...

Source: http://arxiv.org/abs/quant-ph/0502186v2

56
56

Jul 20, 2013
07/13

by
Daniel Burgarth; Sougato Bose

texts

#
eye 56

#
favorite 0

#
comment 0

We suggest a protocol for perfect quantum communication through spin chain channels. By combining a dual-rail encoding with measurements only at the receiving end, we can get conclusively perfect state transfer, whose probability of success can be made arbitrarily close to unity. As an example of such an amplitude delaying channel, we show how two parallel Heisenberg spin chains can be used as quantum wires. Perfect state transfer with a probability of failure lower than P in a Heisenberg chain...

Source: http://arxiv.org/abs/quant-ph/0406112v4

5
5.0

Jun 29, 2018
06/18

by
Christian Arenz; Robin Hillier; Daniel Burgarth

texts

#
eye 5

#
favorite 0

#
comment 0

For finite-dimensional quantum systems, such as qubits, a well established strategy to protect such systems from decoherence is dynamical decoupling. However many promising quantum devices, such as oscillators, are infinite dimensional, for which the question if dynamical decoupling could be applied remained open. Here we first show that not every infinite-dimensional system can be protected from decoherence through dynamical decoupling. Then we develop dynamical decoupling for continuous...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1605.05908

14
14

Jun 28, 2018
06/18

by
Benjamin Dive; Daniel Burgarth; Florian Mintert

texts

#
eye 14

#
favorite 0

#
comment 0

We investigate the problem of what evolutions an open quantum system described by a time-local Master equation can undergo with universal coherent controls. A series of conditions are given which exclude channels from being reachable by any unitary controls, assuming that the coupling to the environment is not being modified. These conditions primarily arise by defining decay rates for the generator of the dynamics of the open system, and then showing that controlling the system can only make...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.07163

53
53

Sep 22, 2013
09/13

by
Daniel Burgarth; Koji Maruyama; Franco Nori

texts

#
eye 53

#
favorite 0

#
comment 0

A number of many-body problems can be formulated using Hamiltonians that are quadratic in the creation and annihilation operators. Here, we show how such quadratic Hamiltonians can be efficiently estimated indirectly, employing very few resources. We find that almost all properties of the Hamiltonian are determined by its surface, and that these properties can be measured even if the system can only be initialised to a mixed state. Therefore our method can be applied to various physical models,...

Source: http://arxiv.org/abs/1004.5018v1

52
52

Sep 23, 2013
09/13

by
Vittorio Giovannetti; Daniel Burgarth; Stefano Mancini

texts

#
eye 52

#
favorite 0

#
comment 0

A chain of interacting spin behaves like a quantum mediator (quantum link) which allows two distant parties that control the ends of the chain to exchange quantum messages. We show that over repeated uses without resetting the study of a quantum link can be connected to correlated quantum channels with finite dimensional environment (finite memory quantum channel). Then, using coding arguments for such kind of channels and results on mixing channels we present a protocol that allows us to...

Source: http://arxiv.org/abs/0810.0170v1

40
40

Sep 23, 2013
09/13

by
Daniel Burgarth; Koji Maruyama; Franco Nori

texts

#
eye 40

#
favorite 0

#
comment 0

Quantum control requires full knowledge of the system many-body Hamiltonian. In many cases this information is not directly available due to restricted access to the system. Here we show how to indirectly estimate all the coupling strengths in a spin chain by measuring one spin at the end of the chain. We also discuss the efficiency of this "quantum inverse problem" and give a numerical example.

Source: http://arxiv.org/abs/0810.2866v2

48
48

Sep 20, 2013
09/13

by
Daniel Burgarth; Vittorio Giovannetti; Sougato Bose

texts

#
eye 48

#
favorite 0

#
comment 0

We present a communication protocol for chains of permanently coupled qubits which achieves perfect quantum state transfer and which is efficient with respect to the number chains employed in the scheme. The system consists of $M$ uncoupled identical quantum chains. Local control (gates, measurements) is only allowed at the sending/receiving end of the chains. Under a quite general hypothesis on the interaction Hamiltonian of the qubits a theorem is proved which shows that the receiver is able...

Source: http://arxiv.org/abs/quant-ph/0410175v3

10
10.0

Jun 27, 2018
06/18

by
Benjamin Dive; Florian Mintert; Daniel Burgarth

texts

#
eye 10

#
favorite 0

#
comment 0

The simulation of quantum systems has been a key aim of quantum technologies for decades, and the generalisation to open systems is necessary to include physically realistic systems. We introduce an approach for quantum simulations of open system dynamics in terms of an environment of minimal size and a time-dependent Hamiltonian. This enables the implementation of a continuous-time simulation with a finite environment, whereas state of the art methods require an infinite environment or only...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1503.01010

52
52

Sep 23, 2013
09/13

by
Xiaoting Wang; Daniel Burgarth; Sophie Schirmer

texts

#
eye 52

#
favorite 0

#
comment 0

Symmetry is a fundamentally important concept in many branches of physics. In this work, we discuss two types of symmetries, external symmetry and internal symmetry, which appear frequently in controlled quantum spin chains and apply them to study various controllability problems. For spin chains under single local end control when external symmetries exists, we can rigorously prove that the system is controllable in each of the invariant subspaces for both XXZ and XYZ chains, but not for XX or...

Source: http://arxiv.org/abs/1202.1033v1

8
8.0

Jun 30, 2018
06/18

by
Robin Hillier; Christian Arenz; Daniel Burgarth

texts

#
eye 8

#
favorite 0

#
comment 0

We discuss a few mathematical aspects of random dynamical decoupling, a key tool procedure in quantum information theory. In particular, we place it in the context of discrete stochastic processes, limit theorems and CPT semigroups on matrix algebras. We obtain precise analytical expressions for expectation and variance of the density matrix and fidelity over time in the continuum-time limit depending on the system Lindbladian, which then lead to rough short-time estimates depending only on...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.7666

105
105

Jul 22, 2013
07/13

by
Ilya Sinaysky; Francesco Petruccione; Daniel Burgarth

texts

#
eye 105

#
favorite 0

#
comment 0

The dynamics of a simple spin chain (2 spins) coupled to bosonic baths at different temperatures is studied. The analytical solution for the reduced density matrix of the system is found. The dynamics and temperature dependence of spin-spin entanglement is analyzed. It is shown that the system converges to a steady-state. If the energy levels of the two spins are different, the steady-state concurrence assumes its maximum at unequal bath temperatures. It is found that a difference in local...

Source: http://arxiv.org/abs/0807.0379v2

76
76

Sep 18, 2013
09/13

by
Heinz-Peter Breuer; Daniel Burgarth; Francesco Petruccione

texts

#
eye 76

#
favorite 0

#
comment 0

The reduced dynamics of a central spin coupled to a bath of N spin-1/2 particles arranged in a spin star configuration is investigated. The exact time evolution of the reduced density operator is derived, and an analytical solution is obtained in the limit of an infinite number of bath spins, where the model shows complete relaxation and partial decoherence. It is demonstrated that the dynamics of the central spin cannot be treated within the Born-Markov approximation. The Nakajima-Zwanzig and...

Source: http://arxiv.org/abs/quant-ph/0401051v2

64
64

Sep 18, 2013
09/13

by
Sougato Bose; Dimitris G. Angelakis; Daniel Burgarth

texts

#
eye 64

#
favorite 0

#
comment 0

We demonstrate a scheme for quantum communication between the ends of an array of coupled cavities. Each cavity is doped with a single two level system (atoms or quantum dots) and the detuning of the atomic level spacing and photonic frequency is appropriately tuned to achieve photon blockade in the array. We show that in such a regime, the array can simulate a dual rail quantum state transfer protocol where the arrival of quantum information at the receiving cavity is heralded through a...

Source: http://arxiv.org/abs/0704.0984v1

30
30

Sep 19, 2013
09/13

by
Kazuya Yuasa; Daniel Burgarth; Vittorio Giovannetti; Hiromichi Nakazato

texts

#
eye 30

#
favorite 0

#
comment 0

A scheme for preparing two fixed non-interacting qubits in a maximally entangled state is presented. By repeating on- and off-resonant scattering of ancilla qubits, the state of the target qubits is driven from an arbitrary initial state into the singlet state with probability 1 (perfect efficiency). Neither the preparation nor the post-selection of the ancilla spin state is required. The convergence from an arbitrary input state to the unique fixed point (mixing property) is proved rigorously,...

Source: http://arxiv.org/abs/0909.3401v2

5
5.0

Jun 30, 2018
06/18

by
Benjamin Dive; Alexander Pitchford; Florian Mintert; Daniel Burgarth

texts

#
eye 5

#
favorite 0

#
comment 0

The ability to perform a universal set of logic gates on a quantum simulator would come close to upgrade it into a universal quantum computer. Knowing how to do this is very hard as it requires a precise knowledge of the simulator. In most cases, it also needs to be itself simulated on a classical computer as part of an optimal control algorithm. This generally can not be done efficiently for the very reason that quantum computers provide an advantage over classical ones. Here we use a...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1701.01723

3
3.0

Jun 30, 2018
06/18

by
Christian Arenz; Benjamin Russell; Daniel Burgarth; Herschel Rabitz

texts

#
eye 3

#
favorite 0

#
comment 0

In this work we derive a lower bound for the minimum time required to implement a target unitary transformation through a classical time-dependent field in a closed quantum system. The bound depends on the target gate, the strength of the internal Hamiltonian and the highest permitted control field amplitude. These findings reveal some properties of the reachable set of operations, explicitly analyzed for a single qubit. Moreover, for fully controllable systems, we identify a lower bound for...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1704.06289

5
5.0

Jun 30, 2018
06/18

by
Jingfu Zhang; Daniel Burgarth; Raymond Laflamme; Dieter Suter

texts

#
eye 5

#
favorite 0

#
comment 0

Universal quantum computation requires the implementation of arbitrary control operations on the quantum register. In most cases, this is achieved by external control fields acting selectively on each qubit to drive single-qubit operations. In combination with a drift Hamiltonian containing interactions between the qubits, this allows the implementation of any required gate operation. Here, we demonstrate an alternative scheme that does not require local control for all qubits: we implement...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.7169

6
6.0

Jun 30, 2018
06/18

by
Christian Arenz; Daniel Burgarth; Paolo Facchi; Robin Hillier

texts

#
eye 6

#
favorite 0

#
comment 0

We investigate the possibility to suppress interactions between a finite dimensional system and an infinite dimensional environment through a fast sequence of unitary kicks on the finite dimensional system. This method, called dynamical decoupling, is known to work for bounded interactions, but physical environments such as bosonic heat baths are usually modelled with unbounded interactions, whence here we initiate a systematic study of dynamical decoupling for unbounded operators. We develop a...

Topics: Quantum Physics, Mathematical Physics, Mathematics

Source: http://arxiv.org/abs/1704.06143

6
6.0

Jun 30, 2018
06/18

by
Christian Arenz; Robin Hillier; Martin Fraas; Daniel Burgarth

texts

#
eye 6

#
favorite 0

#
comment 0

A longstanding challenge in the foundations of quantum mechanics is the verification of alternative collapse theories despite their mathematical similarity to decoherence. To this end, we suggest a novel method based on dynamical decoupling. Experimental observation of nonzero saturation of the decoupling error in the limit of fast decoupling operations can provide evidence for alternative quantum theories. As part of the analysis we prove that unbounded Hamiltonians can always be decoupled,...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1405.7644

63
63

Sep 22, 2013
09/13

by
Kosuke Shizume; Kurt Jacobs; Daniel Burgarth; Sougato Bose

texts

#
eye 63

#
favorite 0

#
comment 0

We analyze a recent protocol for the transmission of quantum states via a dual spin chain [Burgarth and Bose, Phys. Rev. A 71, 052315 (2005)] under the constraint that the receiver's measurement strength is finite. That is, we consider the channel where the ideal, instantaneous and complete von Neumann measurements are replaced with a more realistic continuous measurement. We show that for optimal performance the measurement strength must be "tuned" to the channel spin-spin coupling,...

Source: http://arxiv.org/abs/quant-ph/0702029v1

38
38

Sep 22, 2013
09/13

by
Daniel Burgarth; Sougato Bose; Christoph Bruder; Vittorio Giovannetti

texts

#
eye 38

#
favorite 0

#
comment 0

We give a sufficient criterion that guarantees that a many-body quantum system can be controlled by properly manipulating the (local) Hamiltonian of one of its subsystems. The method can be applied to a wide range of systems: it does not depend on the details of the couplings but only on their associated topology. As a special case, we prove that Heisenberg and Affleck-Kennedy-Lieb-Tasaki chains can be controlled by operating on one of the spins at their ends. In principle, arbitrary quantum...

Source: http://arxiv.org/abs/0805.3975v2

68
68

Sep 19, 2013
09/13

by
Rahel Heule; C. Bruder; Daniel Burgarth; Vladimir M. Stojanovic

texts

#
eye 68

#
favorite 0

#
comment 0

We investigate anisotropic $XXZ$ Heisenberg spin-1/2 chains with control fields acting on one of the end spins, with the aim of exploring local quantum control in arrays of interacting qubits. In this work, which uses a recent Lie-algebraic result on the local controllability of spin chains with "always-on" interactions, we determine piecewise-constant control pulses corresponding to optimal fidelities for quantum gates such as spin-flip (NOT), controlled-NOT (CNOT), and...

Source: http://arxiv.org/abs/1010.5715v1

14
14

Jun 28, 2018
06/18

by
Daniel Burgarth; Vittorio Giovannetti; Airi N. Kato; Kazuya Yuasa

texts

#
eye 14

#
favorite 0

#
comment 0

The problem of estimating a parameter of a quantum system through a series of measurements performed sequentially on a quantum probe is analyzed in the general setting where the underlying statistics is explicitly non-i.i.d. We present a generalization of the central limit theorem in the present context, which under fairly general assumptions shows that as the number $N$ of measurement data increases the probability distribution of functionals of the data (e.g., the average of the data) through...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1507.07634

13
13

Jun 27, 2018
06/18

by
Zoltán Zimborás; Robert Zeier; T. Schulte-Herbrueggen; Daniel Burgarth

texts

#
eye 13

#
favorite 0

#
comment 0

What can one do with a given tunable quantum device? We provide complete symmetry criteria deciding whether some effective target interaction(s) can be simulated by a set of given interactions. Symmetries lead to a better understanding of simulation and permit a reasoning beyond the limitations of the usual explicit Lie closure. Conserved quantities induced by symmetries pave the way to a resource theory for simulability. On a general level, one can now decide equality for any pair of compact...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1504.07734

123
123

Jul 20, 2013
07/13

by
Rahel Heule; C. Bruder; Daniel Burgarth; Vladimir M. Stojanovic

texts

#
eye 123

#
favorite 0

#
comment 0

Motivated by some recent results of quantum control theory, we discuss the feasibility of local operator control in arrays of interacting qubits modeled as isotropic Heisenberg spin chains. Acting on one of the end spins, we aim at finding piecewise-constant control pulses that lead to optimal fidelities for a chosen set of quantum gates. We analyze the robustness of the obtained results f or the gate fidelities to random errors in the control fields, finding that with faster switching between...

Source: http://arxiv.org/abs/1007.2572v2

55
55

Sep 23, 2013
09/13

by
Marco G. Genoni; A. Serafini; M. S. Kim; Daniel Burgarth

texts

#
eye 55

#
favorite 0

#
comment 0

Controllability -- the possibility of performing any target dynamics by applying a set of available operations -- is a fundamental requirement for the practical use of any physical system. For finite-dimensional systems, as for instance spin systems, precise criterions to establish controllability, such as the so called rank criterion, are well known. However most physical systems require a description in terms of an infinite-dimensional Hilbert space whose controllability properties are poorly...

Source: http://arxiv.org/abs/1110.5584v2

52
52

Sep 23, 2013
09/13

by
Daniel Burgarth; Domenico D'Alessandro; Leslie Hogben; Simone Severini; Michael Young

texts

#
eye 52

#
favorite 0

#
comment 0

We study the dynamics of systems on networks from a linear algebraic perspective. The control theoretic concept of controllability describes the set of states that can be reached for these systems. Under appropriate conditions, there is a connection between the quantum (Lie theoretic) property of controllability and the linear systems (Kalman) controllability condition. We investigate how the graph theoretic concept of a zero forcing set impacts the controllability property. In particular, we...

Source: http://arxiv.org/abs/1111.1475v1

95
95

Sep 22, 2013
09/13

by
Daniel Burgarth; Giulio Chiribella; Vittorio Giovannetti; Paolo Perinotti; Kazuya Yuasa

texts

#
eye 95

#
favorite 0

#
comment 0

The paper provides a systematic characterization of quantum ergodic and mixing channels in finite dimensions and a discussion of their structural properties. In particular, we discuss ergodicity in the general case where the fixed point of the channel is not a full-rank (faithful) density matrix. Notably, we show that ergodicity is stable under randomizations, namely that every random mixture of an ergodic channel with a generic channel is still ergodic. In addition, we prove several conditions...

Source: http://arxiv.org/abs/1210.5625v3

48
48

Sep 21, 2013
09/13

by
Daniel Burgarth; Vittorio Giovannetti; Leslie Hogben; Simone Severini; Michael Young

texts

#
eye 48

#
favorite 0

#
comment 0

We design logic circuits based on the notion of zero forcing on graphs; each gate of the circuits is a gadget in which zero forcing is performed. We show that such circuits can evaluate every monotone Boolean function. By using two vertices to encode each logical bit, we obtain universal computation. We also highlight a phenomenon of "back forcing" as a property of each function. Such a phenomenon occurs in a circuit when the input of gates which have been already used at a given time...

Source: http://arxiv.org/abs/1106.4403v4

62
62

Sep 23, 2013
09/13

by
Koji Maruyama; Daniel Burgarth; Akihito Ishizaki; K. Birgitta Whaley; Takeji Takui

texts

#
eye 62

#
favorite 0

#
comment 0

The identification of parameters in the Hamiltonian that describes complex many-body quantum systems is generally a very hard task. Recent attention has focused on such problems of Hamiltonian tomography for networks constructed with two-level systems. For open quantum systems, the fact that injected signals are likely to decay before they accumulate sufficient information for parameter estimation poses additional challenges. In this paper, we consider use of the gateway approach to Hamiltonian...

Source: http://arxiv.org/abs/1111.1062v2

11
11

Jun 30, 2018
06/18

by
Daniel Burgarth; Paolo Facchi; Vittorio Giovannetti; Hiromichi Nakazato; Saverio Pascazio; Kazuya Yuasa

texts

#
eye 11

#
favorite 0

#
comment 0

We show that mere observation of a quantum system can turn its dynamics from a very simple one into a universal quantum computation. This effect, which occurs if the system is regularly observed at short time intervals, can be rephrased as a modern version of Plato's Cave allegory. More precisely, while in the original version of the myth, the reality perceived within the Cave is described by the projected shadows of some more fundamental dynamics which is intrinsically more complex, we found...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1403.5752

49
49

Sep 23, 2013
09/13

by
Elham Hosseini Lapasar; Koji Maruyama; Daniel Burgarth; Takeji Takui; Yasushi Kondo; Mikio Nakahara

texts

#
eye 49

#
favorite 0

#
comment 0

It has been shown that inter-spin interaction strengths in a spins-1/2 chain can be evaluated by accessing one of the edge spins only. We demonstrate this experimentally for the simplest case, a three-spin chain, with nuclear magnetic resonance (NMR) technique. The three spins in the chain interact through nearest-neighbor Ising interactions under site-dependent transverse fields. The employed molecule is an alanine containing three $^{13}$C nuclei, each of which has spin-1/2.

Source: http://arxiv.org/abs/1111.1381v1

4
4.0

Jun 29, 2018
06/18

by
Christian Arenz; Daniel Burgarth; Paolo Facchi; Vittorio Giovannetti; Hiromichi Nakazato; Saverio Pascazio; Kazuya Yuasa

texts

#
eye 4

#
favorite 0

#
comment 0

On the basis of the quantum Zeno effect it has been recently shown [D. K. Burgarth et al., Nat. Commun. 5, 5173 (2014)] that a strong amplitude damping process applied locally on a part of a quantum system can have a beneficial effect on the dynamics of the remaining part of the system. Quantum operations that cannot be implemented without the dissipation become achievable by the action of the strong dissipative process. Here we generalize this idea by identifying decoherence-free subspaces...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1601.01212

5
5.0

Jun 30, 2018
06/18

by
Davide Orsucci; Daniel Burgarth; Paolo Facchi; Hiromichi Nakazato; Saverio Pascazio; Kazuya Yuasa; Vittorio Giovannetti

texts

#
eye 5

#
favorite 0

#
comment 0

The problem of Hamiltonian purification introduced by Burgarth et al. [D. K. Burgarth et al., Nat. Commun. 5, 5173 (2014)] is formalized and discussed. Specifically, given a set of non-commuting Hamiltonians {h1, . . ., hm} operating on a d-dimensional quantum system Hd, the problem consists in identifying a set of commuting Hamiltonians {H1,...,Hm} operating on a larger dE-dimensional system H_{dE} which embeds H_d as a proper subspace, such that hj = PHjP with P being the projection which...

Topics: Quantum Physics, Mathematics, Mathematical Physics

Source: http://arxiv.org/abs/1411.0316

58
58

Sep 21, 2013
09/13

by
Daniel Burgarth; Koji Maruyama; Michael Murphy; Simone Montangero; Tommaso Calarco; Franco Nori; Martin B. Plenio

texts

#
eye 58

#
favorite 0

#
comment 0

We apply quantum control techniques to control a large spin chain by only acting on two qubits at one of its ends, thereby implementing universal quantum computation by a combination of quantum gates on the latter and 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.

Source: http://arxiv.org/abs/0905.3373v2