In this work, we analyze the dependency on the sample's history of relaxation processes of small ... more In this work, we analyze the dependency on the sample's history of relaxation processes of small clusters of interacting particles. These particles interact with each other through the usual Lennard-Jones potential and are confined in a square box of volume V with perfect rigid walls. We use molecular dynamics to simulate a sudden quenching from a very high temperature into the glassy phase and measure the time evolution of the two-time auto-correlation function C(t w , t w + t) after the system has spent a certain time t w in the low temperature phase. We find a strong dependence of C(t w , t w +t) both on t and t w signaling the presence of aging. The scaling law that governs the behavior of C(t w , t w + t) differs from that found by previous works for larger similar systems and in particular displays a dependence on the number of particles N and on the density, ρ = N/V .
Quantum State Transfer and Network Engineering, 2013
This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State ... more This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State Transfer and Network Engineering, edited by G.M. Nikolopoulos and I. Jex [2], where we review our own research about the robustness of spin-chain state-transfer schemes along with other approaches to the topic. Since our own research is documented elsewhere to a large extent we here restrict ourselves to a review of other approaches which might be useful to other researchers in the field.
Quantum state transfer in the presence of static disorder and noise is one of the main challenges... more Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in chains with modified boundaries only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the disorder in the couplings affects the state transfer fidelity depending on the disorder model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in chains with modified boundaries without the demanding engineering of a large number of couplings.
Quantum state transfer in the presence of noise is one of the main challenges for building quantu... more Quantum state transfer in the presence of noise is one of the main challenges for building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static randomness. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in boundary-controlled chains only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the noise in the couplings affects the state transfer fidelity depending on the noise model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in boundary-controlled chains without ...
Journal of Physics A: Mathematical and Theoretical, 2011
One spin excitation states are involved in the transmission of quantum states and entanglement th... more One spin excitation states are involved in the transmission of quantum states and entanglement through a quantum spin chain, the localization properties of these states are crucial to achieve the transfer of information from one extreme of the chain to the other. We investigate the bipartite entanglement and localization of the one excitation states in a quantum XX chain with one impurity. The bipartite entanglement is obtained using the Concurrence and the localization is analyzed using the inverse participation ratio. Changing the strength of the exchange coupling of the impurity allows us to control the number of localized or extended states. Our results show that equally localized states do not possess the same bipartite entanglement and suggest that only a restricted class of localizated states allows the storage and transmission of quantum states.
The transmission of quantum states through spin chains is an important task in the implementation... more The transmission of quantum states through spin chains is an important task in the implementation of quantum information technologies. Many protocols were developed to achieve the high fidelities needed for the state transfer. However, highly demanding and challenging requirements have to be met that are not feasible with present technologies. The main difficulty is the finite precision of the engineering of quantum devices. Very recently, conditions have been identified which enable reliable and robust transmission in the presence of exchange coupling disorder. These conditions only require control of the boundary couplings of the channel rather than the very demanding engineering of the complete set of couplings. In this work we present a systematic study of the principal disordered spin chains that have been analyzed in the literature as possible quantum information transmission channels. Our study focuses on the properties of the chain configuration which ensure, on average, a successful state transmission, but not on the encoding of the state to be transmitted or on means to improve the readout of the arriving signal. We demonstrate that quite different XX spin chain configurations subjected to the same disorder model show qualitatively the same performance. More importantly, that performance, as measured by the fidelity, shows the same scaling behavior with chain length and disorder strength for all systems studied. Our results are helpful in identifying the optimal spin chain for a given quantum information transfer task. In particular, they help in judging whether it is worthwhile to engineer all couplings in the chain as compared to adjusting only the boundary couplings.
Quantum state transfer in the presence of static disorder and noise is one of the main challenges... more Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in chains with modified boundaries only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the disorder in the couplings affects the state transfer fidelity depending on the disorder model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in chains with modified boundaries without the demanding engineering of a large number of couplings.
The transmission of quantum states through spin chains is an important task in the implementation... more The transmission of quantum states through spin chains is an important task in the implementation of quantum information technologies. Many protocols were developed to achieve the high fidelities needed for the state transfer. However, highly demanding and challenging requirements have to be met that are not feasible with present technologies. The main difficulty is the finite precision of the engineering of quantum devices. Very recently, conditions have been identified which enable reliable and robust transmission in the presence of exchange coupling disorder. These conditions only require control of the boundary couplings of the channel rather than the very demanding engineering of the complete set of couplings. In this work we present a systematic study of the principal disordered spin chains that have been analyzed in the literature as possible quantum information transmission channels. Our study focuses on the properties of the chain configuration which ensure, on average, a successful state transmission, but not on the encoding of the state to be transmitted or on means to improve the readout of the arriving signal. We demonstrate that quite different XX spin chain configurations subjected to the same disorder model show qualitatively the same performance. More importantly, that performance, as measured by the fidelity, shows the same scaling behavior with chain length and disorder strength for all systems studied. Our results are helpful in identifying the optimal spin chain for a given quantum information transfer task. In particular, they help in judging whether it is worthwhile to engineer all couplings in the chain as compared to adjusting only the boundary couplings.
Quantum state transfer in the presence of noise is one of the main challenges for building quantu... more Quantum state transfer in the presence of noise is one of the main challenges for building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static randomness. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the
Quantum State Transfer and Network Engineering, 2013
This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State ... more This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State Transfer and Network Engineering, edited by G.M. Nikolopoulos and I. Jex [2], where we review our own research about the robustness of spin-chain state-transfer schemes along with other approaches to the topic. Since our own research is documented elsewhere to a large extent we here restrict ourselves to a review of other approaches which might be useful to other researchers in the field.
The transmission of quantum information between different parts of a quantum computer is of funda... more The transmission of quantum information between different parts of a quantum computer is of fundamental importance. Spin chains have been proposed as quantum channels for transferring information. Different configurations for the spin couplings were proposed in order to optimize the transfer. As imperfections in the creation of these specific spin-coupling distributions can never be completely avoided, it is important to find out which systems are optimally suited for information transfer by assessing their robustness against imperfections or disturbances. We analyze different spin coupling distributions of spin chain channels designed for perfect quantum state transfer. In particular, we study the transfer of an initial state from one end of the chain to the other end. We quantify the robustness of different coupling distributions against perturbations and we relate it to the properties of the energy eigenstates and eigenvalues. We find that the localization properties of the systems play an important role for robust quantum state transfer.
Quantum state transfer in the presence of static disorder and noise is one of the main challenges... more Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in chains with modified boundaries only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the disorder in the couplings affects the state transfer fidelity depending on the disorder model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in chains with modified boundaries without the demanding engineering of a large number of couplings.
Journal of Physics A: Mathematical and Theoretical, 2011
One spin excitation states are involved in the transmission of quantum states and entanglement th... more One spin excitation states are involved in the transmission of quantum states and entanglement through a quantum spin chain, the localization properties of these states are crucial to achieve the transfer of information from one extreme of the chain to the other. We investigate the bipartite entanglement and localization of the one excitation states in a quantum XX chain with one impurity. The bipartite entanglement is obtained using the Concurrence and the localization is analyzed using the inverse participation ratio. Changing the strength of the exchange coupling of the impurity allows us to control the number of localized or extended states. Our results show that equally localized states do not possess the same bipartite entanglement and suggest that only a restricted class of localizated states allows the storage and transmission of quantum states.
In this work, we analyze the dependency on the sample's history of relaxation processes of small ... more In this work, we analyze the dependency on the sample's history of relaxation processes of small clusters of interacting particles. These particles interact with each other through the usual Lennard-Jones potential and are confined in a square box of volume V with perfect rigid walls. We use molecular dynamics to simulate a sudden quenching from a very high temperature into the glassy phase and measure the time evolution of the two-time auto-correlation function C(t w , t w + t) after the system has spent a certain time t w in the low temperature phase. We find a strong dependence of C(t w , t w +t) both on t and t w signaling the presence of aging. The scaling law that governs the behavior of C(t w , t w + t) differs from that found by previous works for larger similar systems and in particular displays a dependence on the number of particles N and on the density, ρ = N/V .
In this work, we analyze the dependency on the sample's history of relaxation processes of small ... more In this work, we analyze the dependency on the sample's history of relaxation processes of small clusters of interacting particles. These particles interact with each other through the usual Lennard-Jones potential and are confined in a square box of volume V with perfect rigid walls. We use molecular dynamics to simulate a sudden quenching from a very high temperature into the glassy phase and measure the time evolution of the two-time auto-correlation function C(t w , t w + t) after the system has spent a certain time t w in the low temperature phase. We find a strong dependence of C(t w , t w +t) both on t and t w signaling the presence of aging. The scaling law that governs the behavior of C(t w , t w + t) differs from that found by previous works for larger similar systems and in particular displays a dependence on the number of particles N and on the density, ρ = N/V .
Quantum State Transfer and Network Engineering, 2013
This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State ... more This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State Transfer and Network Engineering, edited by G.M. Nikolopoulos and I. Jex [2], where we review our own research about the robustness of spin-chain state-transfer schemes along with other approaches to the topic. Since our own research is documented elsewhere to a large extent we here restrict ourselves to a review of other approaches which might be useful to other researchers in the field.
Quantum state transfer in the presence of static disorder and noise is one of the main challenges... more Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in chains with modified boundaries only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the disorder in the couplings affects the state transfer fidelity depending on the disorder model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in chains with modified boundaries without the demanding engineering of a large number of couplings.
Quantum state transfer in the presence of noise is one of the main challenges for building quantu... more Quantum state transfer in the presence of noise is one of the main challenges for building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static randomness. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in boundary-controlled chains only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the noise in the couplings affects the state transfer fidelity depending on the noise model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in boundary-controlled chains without ...
Journal of Physics A: Mathematical and Theoretical, 2011
One spin excitation states are involved in the transmission of quantum states and entanglement th... more One spin excitation states are involved in the transmission of quantum states and entanglement through a quantum spin chain, the localization properties of these states are crucial to achieve the transfer of information from one extreme of the chain to the other. We investigate the bipartite entanglement and localization of the one excitation states in a quantum XX chain with one impurity. The bipartite entanglement is obtained using the Concurrence and the localization is analyzed using the inverse participation ratio. Changing the strength of the exchange coupling of the impurity allows us to control the number of localized or extended states. Our results show that equally localized states do not possess the same bipartite entanglement and suggest that only a restricted class of localizated states allows the storage and transmission of quantum states.
The transmission of quantum states through spin chains is an important task in the implementation... more The transmission of quantum states through spin chains is an important task in the implementation of quantum information technologies. Many protocols were developed to achieve the high fidelities needed for the state transfer. However, highly demanding and challenging requirements have to be met that are not feasible with present technologies. The main difficulty is the finite precision of the engineering of quantum devices. Very recently, conditions have been identified which enable reliable and robust transmission in the presence of exchange coupling disorder. These conditions only require control of the boundary couplings of the channel rather than the very demanding engineering of the complete set of couplings. In this work we present a systematic study of the principal disordered spin chains that have been analyzed in the literature as possible quantum information transmission channels. Our study focuses on the properties of the chain configuration which ensure, on average, a successful state transmission, but not on the encoding of the state to be transmitted or on means to improve the readout of the arriving signal. We demonstrate that quite different XX spin chain configurations subjected to the same disorder model show qualitatively the same performance. More importantly, that performance, as measured by the fidelity, shows the same scaling behavior with chain length and disorder strength for all systems studied. Our results are helpful in identifying the optimal spin chain for a given quantum information transfer task. In particular, they help in judging whether it is worthwhile to engineer all couplings in the chain as compared to adjusting only the boundary couplings.
Quantum state transfer in the presence of static disorder and noise is one of the main challenges... more Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in chains with modified boundaries only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the disorder in the couplings affects the state transfer fidelity depending on the disorder model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in chains with modified boundaries without the demanding engineering of a large number of couplings.
The transmission of quantum states through spin chains is an important task in the implementation... more The transmission of quantum states through spin chains is an important task in the implementation of quantum information technologies. Many protocols were developed to achieve the high fidelities needed for the state transfer. However, highly demanding and challenging requirements have to be met that are not feasible with present technologies. The main difficulty is the finite precision of the engineering of quantum devices. Very recently, conditions have been identified which enable reliable and robust transmission in the presence of exchange coupling disorder. These conditions only require control of the boundary couplings of the channel rather than the very demanding engineering of the complete set of couplings. In this work we present a systematic study of the principal disordered spin chains that have been analyzed in the literature as possible quantum information transmission channels. Our study focuses on the properties of the chain configuration which ensure, on average, a successful state transmission, but not on the encoding of the state to be transmitted or on means to improve the readout of the arriving signal. We demonstrate that quite different XX spin chain configurations subjected to the same disorder model show qualitatively the same performance. More importantly, that performance, as measured by the fidelity, shows the same scaling behavior with chain length and disorder strength for all systems studied. Our results are helpful in identifying the optimal spin chain for a given quantum information transfer task. In particular, they help in judging whether it is worthwhile to engineer all couplings in the chain as compared to adjusting only the boundary couplings.
Quantum state transfer in the presence of noise is one of the main challenges for building quantu... more Quantum state transfer in the presence of noise is one of the main challenges for building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static randomness. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the
Quantum State Transfer and Network Engineering, 2013
This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State ... more This is a shortened and slightly edited version of a chapter [1] in the collection Quantum State Transfer and Network Engineering, edited by G.M. Nikolopoulos and I. Jex [2], where we review our own research about the robustness of spin-chain state-transfer schemes along with other approaches to the topic. Since our own research is documented elsewhere to a large extent we here restrict ourselves to a review of other approaches which might be useful to other researchers in the field.
The transmission of quantum information between different parts of a quantum computer is of funda... more The transmission of quantum information between different parts of a quantum computer is of fundamental importance. Spin chains have been proposed as quantum channels for transferring information. Different configurations for the spin couplings were proposed in order to optimize the transfer. As imperfections in the creation of these specific spin-coupling distributions can never be completely avoided, it is important to find out which systems are optimally suited for information transfer by assessing their robustness against imperfections or disturbances. We analyze different spin coupling distributions of spin chain channels designed for perfect quantum state transfer. In particular, we study the transfer of an initial state from one end of the chain to the other end. We quantify the robustness of different coupling distributions against perturbations and we relate it to the properties of the energy eigenstates and eigenvalues. We find that the localization properties of the systems play an important role for robust quantum state transfer.
Quantum state transfer in the presence of static disorder and noise is one of the main challenges... more Quantum state transfer in the presence of static disorder and noise is one of the main challenges in building quantum computers. We compare the quantum state transfer properties for two classes of qubit chains under the influence of static disorder. In fully engineered chains all nearest-neighbor couplings are tuned in such a way that a single-qubit state can be transferred perfectly between the ends of the chain, while in chains with modified boundaries only the two couplings between the transmitting and receiving qubits and the remainder of the chain can be optimized. We study how the disorder in the couplings affects the state transfer fidelity depending on the disorder model and strength as well as the chain type and length. We show that the desired level of fidelity and transfer time are important factors in designing a chain. In particular we demonstrate that transfer efficiency comparable or better than that of the most robust engineered systems can also be reached in chains with modified boundaries without the demanding engineering of a large number of couplings.
Journal of Physics A: Mathematical and Theoretical, 2011
One spin excitation states are involved in the transmission of quantum states and entanglement th... more One spin excitation states are involved in the transmission of quantum states and entanglement through a quantum spin chain, the localization properties of these states are crucial to achieve the transfer of information from one extreme of the chain to the other. We investigate the bipartite entanglement and localization of the one excitation states in a quantum XX chain with one impurity. The bipartite entanglement is obtained using the Concurrence and the localization is analyzed using the inverse participation ratio. Changing the strength of the exchange coupling of the impurity allows us to control the number of localized or extended states. Our results show that equally localized states do not possess the same bipartite entanglement and suggest that only a restricted class of localizated states allows the storage and transmission of quantum states.
In this work, we analyze the dependency on the sample's history of relaxation processes of small ... more In this work, we analyze the dependency on the sample's history of relaxation processes of small clusters of interacting particles. These particles interact with each other through the usual Lennard-Jones potential and are confined in a square box of volume V with perfect rigid walls. We use molecular dynamics to simulate a sudden quenching from a very high temperature into the glassy phase and measure the time evolution of the two-time auto-correlation function C(t w , t w + t) after the system has spent a certain time t w in the low temperature phase. We find a strong dependence of C(t w , t w +t) both on t and t w signaling the presence of aging. The scaling law that governs the behavior of C(t w , t w + t) differs from that found by previous works for larger similar systems and in particular displays a dependence on the number of particles N and on the density, ρ = N/V .
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