Qutip/Qutip: Qutip-4.0.0

Nation, Paul; Vardhan, Anubhav; Pitchford, Alexander; Granade, Chris; markusbaden,; Grimsmo, Arne L.; Migdał, Piotr; kafischer,; Vasilyev, Denis V.; Criger, Ben; Feist, Johannes; alexbrc,; Henneke, Felix; Meiser, Dominic; Ziem, Florestan; nwlambert,; Krastanov, Stefan; Brierley, Richard; Heeres, Reinier; Hörsch, Jonas; Qi, Qi; Whalen, S. J.; Tezak, Nikolas; Neergaard-Nielsen, Jonas S.; Hontz, Eric; Adriaan,

doi:10.5281/zenodo.220867

Cited by 4 publications

(5 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In order to study the tightness of the bounds ( 2) and ( 6) we employ in this section numerical minimization of the infidelity using the GRAPE algorithm in the QuTip control package [59,60]. We begin by analyzing the bound (6), i.e., the case in which the control field amplitude is not constrained such that the speed limits only arise from the limited strength of the drift Hamiltonian.…”

Section: Tightness Of the Bound And Pareto Optimal Controlmentioning

confidence: 99%

The roles of drift and control field constraints upon quantum control speed limits

et al. 2017

View full text Add to dashboard Cite

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 the time at which all unitary gates become reachable. We use numerical gate optimization in order to study the tightness of the obtained bounds. It is shown that in the single qubit case our analytical findings describe the relationship between the highest control field amplitude and the minimum evolution time remarkably well. Finally, we discuss both challenges and ways forward for obtaining tighter bounds for higher dimensional systems, offering a discussion about the mathematical form and the physical meaning of the bound.

show abstract

Section: Tightness Of the Bound And Pareto Optimal Controlmentioning

confidence: 99%

The roles of drift and control field constraints upon quantum control speed limits

et al. 2017

View full text Add to dashboard Cite

show abstract

“…The optimal control software QTRL [25] generally optimises control pulses by minimising a given fidelity, which by default is chosen to be a suitable distance from a target quantum object (either a state or a unitary operator). For the purpose of the present work, we needed to implement a completely different fidelity, namely the negative of the QFI F c,λ described in the main text.…”

Section: Computation Of the Qfi And Its Gradientmentioning

confidence: 99%

“…Numerical simulation for a longer chain.-Let us now look at longer chains. We implement the crucial control step of the above estimation procedure using the optimal control software QTRL, which is a part of the QuTip control package [24,25]. In addition to the existing software, we have implemented an exact gradient of the QFI in a way applicable to an arbitrary quantum system probed by a single spin.…”

mentioning

confidence: 99%

Remote parameter estimation in a quantum spin chain enhanced by local control

2017

View full text Add to dashboard Cite

EPSRC Grant No. EP/M01634X/1We study the interplay of control and parameter estimation on a quantum spin chain. A single qubit probe is attached to one end of the chain, while we wish to estimate a parameter on the other end. We find that control on the probe qubit can substantially improve the estimation performance and discover some interesting connections to quantum state transferauthorsversionPeer reviewe

show abstract

“…The idea of OCT is to maximize or minimize a given cost functional based on the Pontryagin maximum principle. Typically this is done by numerically searching for global optima using a gradient based approach such as gradient ascent pulse engineering (GRAPE) [42], which is implemented in the control package in QuTiP [43,44]. Here we use the GRAPE algorithm in order to find the pulse Ω(t) that maximizes the fidelity.…”

mentioning

confidence: 99%

“…, Ω n the piecewise constant pulse amplitudes, it is straightforward to calculate the gradient of F with respect to Ω i , noting that an expression for ∂U (T ) ∂Ωi can be found in [45]. After having modified the gradient expression in [43,44] accordingly, we maximized F for a total evolution time FIG. 5: online) Pulse envelope implementing the ccz gate as a function of time.…”

mentioning

confidence: 99%

Fast microwave-driven three-qubit gates for cavity-coupled superconducting qubits

et al. 2017

Self Cite

View full text Add to dashboard Cite

Although single and two-qubit gates are sufficient for universal quantum computation, single-shot three-qubit gates greatly simplify quantum error correction schemes and algorithms. We design fast, high-fidelity three-qubit entangling gates based on microwave pulses for transmon qubits coupled through a superconducting resonator. We show that when interqubit frequency differences are comparable to single-qubit anharmonicities, errors occur primarily through a single unwanted transition. This feature enables the design of fast three-qubit gates based on simple analytical pulse shapes that are engineered to minimize such errors. We show that a three-qubit ccz gate can be performed in 260 ns with fidelities exceeding 99.38%, or 99.99% with numerical optimization.Quantum information processing is one of the most exciting and rapidly growing fields of modern science, in large part due to quantum algorithms, which promise exponential speedup in solving important problems. Quantum two-level systems (qubits) are the fundamental carriers of quantum information, and among the most promising of these are qubits based on superconducting circuits [1,2]. Such an architecture is attractive because of the mature circuit fabrication technology and the ability to couple qubits together via resonators to implement logic gates [3].For universal quantum computing, a certain set of high-fidelity logic gates suffices to implement any algorithm; this set is comprised of single-qubit gates along with one maximally entangling two-qubit gate. Threequbit gates, which play a prominent role in algorithms, can be decomposed in terms of a sequence of single-and two-qubit gates [4]. In the case of a maximally entangling three-qubit control-control-z (ccz) gate (described below), one must perform seven single-qubit gates and six entangling two-qubit gates, as shown in Fig. 1. The large number of gates needed makes it natural to explore whether a direct, single-shot three-qubit gate is preferable in terms of speed and fidelity.There are two ways to implement logic gates in superconducting qubit systems. One is via tuning of the energy levels, which brings states into and out of resonance. The other is via oscillating microwave fields that induce transitions between energy levels, which offers the advantage of less susceptibility to charge noise. Both approaches face the challenge of spectral crowding in these systems, especially in the context of superconducting transmon qubits where each qubit is a weakly anharmonic oscillator out of which the two lowest levels are selected to encode information [5]. In the case of many qubits coupled together, there is a large number of closely spaced transitions that need to be avoided during quantum gate operations. Generically, a way to avoid unwanted transitions is to consider the time-energy uncertainty principle, which tells us to make the operations slow. In realistic systems, however, this is not an option, as we need to perform operations at a time scale that is much faster than decay and decoherence. ...

show abstract

Qutip/Qutip: Qutip-4.0.0

Cited by 4 publications

References 0 publications

The roles of drift and control field constraints upon quantum control speed limits

The roles of drift and control field constraints upon quantum control speed limits

Remote parameter estimation in a quantum spin chain enhanced by local control

Fast microwave-driven three-qubit gates for cavity-coupled superconducting qubits

Contact Info

Product

Resources

About