Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Journal of Physics Conference Series

Examination of logic operations with silent phase qubit

N. V. Klenov, Victor K. Kornev, A. Vedyayev, Natalia Ryzhanova, Н. Г. Пугач, T. S. Rumyantseva

Published Feb 1, 2008• 17 citations
Publisher

Abstract

Reduced control Hamiltonian of the silent phase qubit has been found and dependence of the Hamiltonian matrix elements on applied magnetic field has been analyzed. The obtained results yield in concept of qubit logic operations accomplished by means of magnetic field application. One can propose a set of the qubits, each designed for specific logic operation. The qubit logic specialization may be fixed by both the junction current-phase relation and the characteristic Josephson-to-Coulomb energy ratio s. As current-phase relation is assigned, the qubit specialization can be tuned by the ratio s which varies with Josephson junction area. Examples of some logic operations are considered. Estimation of both the decoherence time and the quality factor Q has been obtained for such a qubit based on high-T c superconductors, which could provide the required current-phase relation.

DOI
10.1088/1742-6596/97/1/012037

Related papers

Josephson-Junction Qubits

Yuriy Makhlin, Gerd Schön, Alexander Shnirman

Among the potential physical implementations of quantum bits (qubits) solid state devices appear most promising for large scale applications and integration in electronic circuits. Devices based on low-capacitance Josephson junctions exploit the coherence of the superconducting state, combined with the possibility to control individual charges by Coulomb blockade effects. The logical states in these systems differ by one Cooper-pair charge. Single- and two-bit operations can be performed by applying a sequence of gate voltages. The phase coherence time is sufficiently long to allow a series of these steps. If, in addition, the strength of the Josephson coupling is controlled (e.g. by currents in SQUID loops) the system is ideal for quantum computation. Recent experiments by Nakamura et al. show the feasibility of this approach. In addition to the manipulations of qubits the resulting quantum state has to be read out. This quantum measurement process can be accomplished by coupling a single-electron transistor (SET) capacitively to the qubit. We investigate the process by analyzing the time-evolution of the density matrix of the coupled system. The measurement process is characterized by three time scales: the dephasing time, which is fast when a dissipative current flows in the SET, a longer ‘measurement time’ needed to read out the signal, and a third, even longer ‘mixing time’, characterizing measurement induced transitions which destroy the information about the initial quantum state. The noise spectrum of the current in the SET displays these time scales and allows their direct observation.

Fortschritte der Physik•Sep 1, 2000•9 citations

Silent phase qubit based on d -wave Josephson junctions

M. H. S. Amin, Anatoly Yu. Smirnov, Alexandre M. Zagoskin +4 more

A flux qubit is designed and fabricated that capitalizes on intrinsic properties of submicron YBCO (yttrium-barium-copper oxide high-${T}_{c}$ superconductor) grain boundary junctions. The operating point is protected from the fluctuations of the external fields, already on the classical level. The effects of external perturbations only appear in the third or fourth order, depending on the character of the coupling. The estimates of the decoherence due to fluctuations of the external flux show that an experimental observation of coherent quantum tunneling and Rabi oscillations in the system is feasible.

arXiv:cond-mat/0310224•Physical Review B•Feb 24, 2005•62 citations

Engineering superconducting qubits : towards a quantum machine

Joachim Sjöstrand

A quantum computer is an information processing machine, much like an ordinary classical computer, but its function is based on quantum mechanical principles. To be able to construct such a machine would be a fantastic accomplishment---to have total control over a quantum system is a dream for both physicists and science-fiction enthusiasts. The basic information unit in a quantum computer is the quantum bit, or qubit for short. A quantum computer consists of many coupled qubits. To get a single qubit to work properly, would be a major step towards building this machine. Here we study two different qubit ideas. The central element in both setups is the superconducting tunnel junction---the Josephson junction. By connecting the Josephson junctions to standard electronics in a clever way, a qubit can be realised. With these constructions it is in principle very easy to manipulate and read out the quantum probabilities, by varying voltages and currents in time. However, this ease of manipulation has a cost: strong interactions with uncontrolled degrees of freedom of the environment transfer information from the qubit. For superconducting qubits this decoherence is typically very fast. There are ways to deal with the decoherence. One way is to tune the circuit parameters so that the decoherence becomes minimal. Another way is to engineer the qubits so fast so that the effect of decoherence becomes small. In this thesis, we will apply both these strategies. Specifically, the measurement speed of the second qubit we study, turns out to be very sensitive to the topology of the phase space of the detector variables.

•Jan 1, 2006•1 citation

Josephson-Junction Qubits and the Readout Process by Single-Electron Transistors

Yuriy Makhlin, Gerd Schön, Alexander Shnirman

Several physical realizations of quantum bits have been proposed. Of those, nano-electronic devices appear most suitable for large-scale integration and potential applications. We suggest to use low-capacitance Josephson junctions, exploiting the coherence of tunneling in the superconducting state combined with the possibility to control individual charges by Coulomb blockade effects (cond-mat/9706016,cond-mat/9808067). These systems constitute quantum bits, with logical states differing by one Cooper-pair charge. Single- and two-bit operations can be performed by applying a sequence of gate voltages. The phase coherence time is sufficiently long to allow a series of these steps. In addition to the manipulation of qubits the resulting quantum state has to be read out. This can be accomplished by coupling a single-electron transistor capacitively to the qubit (cond-mat/9801125). To describe this quantum measurement process we study the time evolution of the density matrix of the coupled system. Only when a transport voltage is turned on, the transistor destroys the phase coherence of the qubit; in this case within a short time. The measurement is accomplished after a longer time scale, when the signal resolves the different quantum states. At still longer times the measurement process itself destroys the information about the initial state. We present a suitable set of system parameters, which can be realized by present-day technology.

arXiv:cond-mat/9811029•Nov 3, 1998•10 citations

Nano-electronic circuits as quantum bits

Yuriy Makhlin, Gerd Schön, Alexander Shnirman

Quantum information processing systems can be used in a variety of applications. Among proposed realizations of quantum bits nano-electronic circuits appear most promising for integration in electronic circuits and large-scale applications. We discuss Josephson junction circuits in two regimes where they can be used for quantum computing. In one limit, two logic states of the quantum bit differ by a Cooper pair charge, 2e, on a superconducting island. In the other limit different magnetic fluxes penetrate a superconducting loop in two states. Single-qubit and two-qubit logic operations can be performed by means of voltage or current pulses. Weak coupling to the environment allows a series of these elementary steps before the phase coherence is lost. To read out the result of the computation a quantum measurement is needed. For charge qubits this can be accomplished by coupling a single-electron transistor (SET) capacitively to the qubit. Monitoring the current in the transistor one can extract the information about the state of the qubit. We discuss recent experiments and present a suitable set of circuit parameters available with the present-day technology.

IEEE International Symposium on Circuits and Systems proceedings•Nov 7, 2002•4 citations

Superconducting Nb Nanobridges for Reduced Footprint and Efficient Next-Generation Electronics

Jonathan A. Collins, Calum Rose, A. Casaburi

We optimized a process to reliably fabricate thin Nb nanobridge weak links having a physical size comparable with Nb coherence length ξ(4.2K) ∼16 nm, controlled degraded superconductivity with respect to the electrodes, and excellent edge roughness. We then investigated the feasibility to use these nanobridges as the Josephson element for reduced footprints and efficient next-generation single flux quantum (SFQ) logic electronics. First of all, we demonstrated that in such thin Nb nanobridges, there is no thermal hysteresis in the current–voltage characteristics (IVC) that instead is usually observed in other weak links and prevents their use in SFQ electronics. We fitted the experimental IVCs of nanobridges with the resistively shunted junction model implemented with piecewise linear current–phase relation (CPR) finding a very good agreement with data. This allowed us to infer the CPR parameters and evaluate the product of critical current and normal resistance,IcRn∼mV, at varying temperatures. Using these data, we simulated the generation of voltage pulses at varying CPRs and verified that they still have a quantized area equal to the magnetic flux quantum Φ0and the productIcRnallows for speed of operationIcRN/ Φ0$\gg $100 GHz. Moreover, their critical currentIc$\approx $100$\mu $A, comparable with that of tunnel Josephson junctions (JJs) used in SFQ electronics, is orders of magnitude larger than thermal current noiseITN= (2π / Φ0)kBT$\approx $0.2$\mu $A at temperatureT= 4.2 K, for stable and, at the same time, efficient operation with energy per switch of onlyEJ≈ICΦ0$\mathbin{\hbox{$\buildrel<\over {\smash{\scriptstyle \sim}\vphantom{_x}}$}} $1 aJ. To assess the potential use of these nanobridges in SFQ logic electronics with a large number of elements, we used an open-source simulation software (JSim) to simulate the behavior of a standard DC-to-SFQ converter circuit. From the simulation made by implementing the CPR inferred from experimental data, we observed that the circuit behaves exactly as intended. Our results strongly suggest that these nanobridges can be used to develop large-scale SFQ electronics with several advantages over tunnel JJs. The reduced footprint, just one-third or less than standard tunnel JJs, and simplified fabrication process, with only 2 steps involved against typically ∼20 for tunnel JJs, could allow for a better fabrication tolerance, higher control on operation parameters, higher circuit density, and easier integration with other technology platforms. These characteristics could be very appealing also to replace tunnel JJs in quantum technology devices like transmon qubits and superconducting parametric amplifiers.

IEEE Transactions on Applied Superconductivity•Nov 4, 2022•8 citations
Reduced control Hamiltonian of the silent phase qubit has been found and dependence of the Hamiltonian matrix elements on applied magnetic field has been analyzed. The obtained results yield in concept of qubit logic operations accomplished by means of magnetic field application. One can propose a set of the qubits, each designed for specific logic operation. The qubit logic specialization may be fixed by both the junction current-phase relation and the characteristic Josephson-to-Coulomb energy ratio s. As current-phase relation is assigned, the qubit specialization can be tuned by the ratio s which varies with Josephson junction area. Examples of some logic operations are considered. Estimation of both the decoherence time and the quality factor Q has been obtained for such a qubit based on high-T c superconductors, which could provide the required current-phase relation.
Among the potential physical implementations of quantum bits (qubits) solid state devices appear most promising for large scale applications and integration in electronic circuits. Devices based on low-capacitance Josephson junctions exploit the coherence of the superconducting state, combined with the possibility to control individual charges by Coulomb blockade effects. The logical states in these systems differ by one Cooper-pair charge. Single- and two-bit operations can be performed by applying a sequence of gate voltages. The phase coherence time is sufficiently long to allow a series of these steps. If, in addition, the strength of the Josephson coupling is controlled (e.g. by currents in SQUID loops) the system is ideal for quantum computation. Recent experiments by Nakamura et al. show the feasibility of this approach. In addition to the manipulations of qubits the resulting quantum state has to be read out. This quantum measurement process can be accomplished by coupling a single-electron transistor (SET) capacitively to the qubit. We investigate the process by analyzing the time-evolution of the density matrix of the coupled system. The measurement process is characterized by three time scales: the dephasing time, which is fast when a dissipative current flows in the SET, a longer ‘measurement time’ needed to read out the signal, and a third, even longer ‘mixing time’, characterizing measurement induced transitions which destroy the information about the initial quantum state. The noise spectrum of the current in the SET displays these time scales and allows their direct observation.
A flux qubit is designed and fabricated that capitalizes on intrinsic properties of submicron YBCO (yttrium-barium-copper oxide high-Tc{T}_{c}Tc​ superconductor) grain boundary junctions. The operating point is protected from the fluctuations of the external fields, already on the classical level. The effects of external perturbations only appear in the third or fourth order, depending on the character of the coupling. The estimates of the decoherence due to fluctuations of the external flux show that an experimental observation of coherent quantum tunneling and Rabi oscillations in the system is feasible.
A quantum computer is an information processing machine, much like an ordinary classical computer, but its function is based on quantum mechanical principles. To be able to construct such a machine would be a fantastic accomplishment---to have total control over a quantum system is a dream for both physicists and science-fiction enthusiasts. The basic information unit in a quantum computer is the quantum bit, or qubit for short. A quantum computer consists of many coupled qubits. To get a single qubit to work properly, would be a major step towards building this machine. Here we study two different qubit ideas. The central element in both setups is the superconducting tunnel junction---the Josephson junction. By connecting the Josephson junctions to standard electronics in a clever way, a qubit can be realised. With these constructions it is in principle very easy to manipulate and read out the quantum probabilities, by varying voltages and currents in time. However, this ease of manipulation has a cost: strong interactions with uncontrolled degrees of freedom of the environment transfer information from the qubit. For superconducting qubits this decoherence is typically very fast. There are ways to deal with the decoherence. One way is to tune the circuit parameters so that the decoherence becomes minimal. Another way is to engineer the qubits so fast so that the effect of decoherence becomes small. In this thesis, we will apply both these strategies. Specifically, the measurement speed of the second qubit we study, turns out to be very sensitive to the topology of the phase space of the detector variables.
Several physical realizations of quantum bits have been proposed. Of those, nano-electronic devices appear most suitable for large-scale integration and potential applications. We suggest to use low-capacitance Josephson junctions, exploiting the coherence of tunneling in the superconducting state combined with the possibility to control individual charges by Coulomb blockade effects (cond-mat/9706016,cond-mat/9808067). These systems constitute quantum bits, with logical states differing by one Cooper-pair charge. Single- and two-bit operations can be performed by applying a sequence of gate voltages. The phase coherence time is sufficiently long to allow a series of these steps. In addition to the manipulation of qubits the resulting quantum state has to be read out. This can be accomplished by coupling a single-electron transistor capacitively to the qubit (cond-mat/9801125). To describe this quantum measurement process we study the time evolution of the density matrix of the coupled system. Only when a transport voltage is turned on, the transistor destroys the phase coherence of the qubit; in this case within a short time. The measurement is accomplished after a longer time scale, when the signal resolves the different quantum states. At still longer times the measurement process itself destroys the information about the initial state. We present a suitable set of system parameters, which can be realized by present-day technology.
Quantum information processing systems can be used in a variety of applications. Among proposed realizations of quantum bits nano-electronic circuits appear most promising for integration in electronic circuits and large-scale applications. We discuss Josephson junction circuits in two regimes where they can be used for quantum computing. In one limit, two logic states of the quantum bit differ by a Cooper pair charge, 2e, on a superconducting island. In the other limit different magnetic fluxes penetrate a superconducting loop in two states. Single-qubit and two-qubit logic operations can be performed by means of voltage or current pulses. Weak coupling to the environment allows a series of these elementary steps before the phase coherence is lost. To read out the result of the computation a quantum measurement is needed. For charge qubits this can be accomplished by coupling a single-electron transistor (SET) capacitively to the qubit. Monitoring the current in the transistor one can extract the information about the state of the qubit. We discuss recent experiments and present a suitable set of circuit parameters available with the present-day technology.
We optimized a process to reliably fabricate thin Nb nanobridge weak links having a physical size comparable with Nb coherence length ξ(4.2K) ∼16 nm, controlled degraded superconductivity with respect to the electrodes, and excellent edge roughness. We then investigated the feasibility to use these nanobridges as the Josephson element for reduced footprints and efficient next-generation single flux quantum (SFQ) logic electronics. First of all, we demonstrated that in such thin Nb nanobridges, there is no thermal hysteresis in the current–voltage characteristics (IVC) that instead is usually observed in other weak links and prevents their use in SFQ electronics. We fitted the experimental IVCs of nanobridges with the resistively shunted junction model implemented with piecewise linear current–phase relation (CPR) finding a very good agreement with data. This allowed us to infer the CPR parameters and evaluate the product of critical current and normal resistance,IcRn∼mV, at varying temperatures. Using these data, we simulated the generation of voltage pulses at varying CPRs and verified that they still have a quantized area equal to the magnetic flux quantum Φ0and the productIcRnallows for speed of operationIcRN/ Φ0$\gg 100GHz.Moreover,theircriticalcurrentIc100 GHz. Moreover, their critical currentIc100GHz.Moreover,theircriticalcurrentIc\approx 100100100\mu A,comparablewiththatoftunnelJosephsonjunctions(JJs)usedinSFQelectronics,isordersofmagnitudelargerthanthermalcurrentnoiseITN=(2π/Φ0)kBTA, comparable with that of tunnel Josephson junctions (JJs) used in SFQ electronics, is orders of magnitude larger than thermal current noiseITN= (2π / Φ0)kBTA,comparablewiththatoftunnelJosephsonjunctions(JJs)usedinSFQelectronics,isordersofmagnitudelargerthanthermalcurrentnoiseITN=(2π/Φ0)kBT\approx 0.20.20.2\mu AattemperatureT=4.2K,forstableand,atthesametime,efficientoperationwithenergyperswitchofonlyEJ≈ICΦ0A at temperatureT= 4.2 K, for stable and, at the same time, efficient operation with energy per switch of onlyEJ≈ICΦ0AattemperatureT=4.2K,forstableand,atthesametime,efficientoperationwithenergyperswitchofonlyEJ≈ICΦ0\mathbin{\hbox{$\buildrel<\over {\smash{\scriptstyle \sim}\vphantom{_x}}$}} $1 aJ. To assess the potential use of these nanobridges in SFQ logic electronics with a large number of elements, we used an open-source simulation software (JSim) to simulate the behavior of a standard DC-to-SFQ converter circuit. From the simulation made by implementing the CPR inferred from experimental data, we observed that the circuit behaves exactly as intended. Our results strongly suggest that these nanobridges can be used to develop large-scale SFQ electronics with several advantages over tunnel JJs. The reduced footprint, just one-third or less than standard tunnel JJs, and simplified fabrication process, with only 2 steps involved against typically ∼20 for tunnel JJs, could allow for a better fabrication tolerance, higher control on operation parameters, higher circuit density, and easier integration with other technology platforms. These characteristics could be very appealing also to replace tunnel JJs in quantum technology devices like transmon qubits and superconducting parametric amplifiers.