Generation of large coherent states by bang–bang control of a trapped-ion oscillator

Abstract

Fast control of quantum systems is essential to make use of quantum properties before they degrade by decoherence. This is important for quantum-enhanced information processing, as well as for pushing quantum systems towards the boundary between quantum and classical physics. ‘Bang–bang' control attains the ultimate speed limit by making large changes to control fields much faster than the system can respond, but is often challenging to implement experimentally. Here we demonstrate bang–bang control of a trapped-ion oscillator using nanosecond switching of the trapping potentials. We perform controlled displacements with which we realize coherent states with up to 10,000 quanta of energy. We use these displaced states to verify the form of the ion-light interaction at high excitations far outside the usual regime of operation. These methods provide new possibilities for quantum-state manipulation and generation, alongside the potential for a significant increase in operational clock speed for trapped-ion quantum information processing.

Fault-tolerant preparation of approximate GKP states

“…gate locations both before and after the controlled displacement gate). Instead, we analytically computed the error probabilities for each Pauli operator (using the depolarizing noise model described above) immediately after the first CNOT gate, before both measurement locations and before the phase gate 10 . At each location, all possible Pauli operators based on their associated probabilities were added.…”

“…The fault-tolerant state preparation of approximate GKP states presented in this work is tailored to protocols that use phase estimation. An interesting direction for future work would be to find fault-tolerant implementations for preparing approximate GKP states that apply to broader schemes such as those found in [10,13]. In addition, fault-tolerant state preparation protocols for hexagonal GKP codes could be analyzed since these offer better error correction capabilities than GKP codes on a square lattice.…”

“…Given the above, it is clear that the fault-tolerant preparation of encoded GKP states is an important problem that needs to be addressed. Various proposals for preparing GKP states have been outlined [3,[8][9][10][11][12][13][14][15]. However to our knowledge, no clear definitions for fault-tolerantly preparing GKP states using qubit-cavity couplings have been proposed.…”

Single-ion addressing via trap potential modulation in global optical fields

“…Similarly, the modest speed of the sequences used in these demonstrations is currently constrained by the ≈100 kHz sample rate of our DACs, but this is not a fundamental limit. Adiabatic modulations of the trapping potential can be achieved in a few microseconds with faster DACs, while even faster diabatic changes can in principle be realized with finely sampled waveforms [34][35][36]. Because the laser pulses typically require durations of several microseconds, it should be possible to perform SIAPM sequences during intervals only about twice as long as that of an individual pulse.…”

Classical and quantum dynamics of a trapped ion coupled to a charged nanowire

“…A disadvantage of the optical field is that it interacts with an electric dipole or quadrupole moment of the atomic ion and the oscillator states prepared in this way are typically limited to excitations of <20 quanta. The charged nanowire, on the other hand, acts directly on the electric monopole and therefore large-amplitude coherent states can be created without the need of electronics for fast switching trapping potentials [44] as seen in figure 6. This figure shows the Fock distribution and Wigner function of a large coherent state with = n 45 after 70 μs of driving dynamics.…”