A major barrier for the development of new quantum technologies is fast and robust methods for preparing and manipulating complex quantum states. To date preparation and manipulation of quantum systems has primarily been done using adiabatic processes. These adiabatic processes while robust have significant disadvantages such as their requiring long process times, a further drawback is that the system-environment interaction over these these long process times can lead to loss of coherence of the state of the system. A new area of study to achieve the robustness of adiabatic schemes but in time-scales much shorter is "Shortcuts to Adiabaticity" (STA). These STA techniques provide new methods for the manipulation of quantum systems that achieve high-fidelity state transfers in much shorter times. The aim of this thesis is to use STA and related methods for many particle systems. A method for manipulating a gas of fermions is developed using Pauli blocking and it’s robustness in the presence of temperature and different particle number investigated. A novel method for trapping and cooling particles using atom-diode and reflecting atomic mirror is investigated, both the classical and quantum cases are simulated. A method for transporting atoms and condensates across an optical lattice using invariant based inverse engineering is developed. Finally we look at non-hermitian potentials and design particular potentials that result in desirable asymmetries in the transmission and reflection of incident particles.
A major barrier for the development of new quantum technologies is fast and robust methods for preparing and manipulating complex quantum states. To date preparation and manipulation of quantum systems has primarily been done using adiabatic processes. These adiabatic processes while robust have significant disadvantages such as their requiring long process times, a further drawback is that the system-environment interaction over these these long process times can lead to loss of coherence of the state of the system. A new area of study to achieve the robustness of adiabatic schemes but in time-scales much shorter is "Shortcuts to Adiabaticity" (STA). These STA techniques provide new methods for the manipulation of quantum systems that achieve high-fidelity state transfers in much shorter times. The aim of this thesis is to use STA and related methods for many particle systems. A method for manipulating a gas of fermions is developed using Pauli blocking and it’s robustness in the presence of temperature and different particle number investigated. A novel method for trapping and cooling particles using atom-diode and reflecting atomic mirror is investigated, both the classical and quantum cases are simulated. A method for transporting atoms and condensates across an optical lattice using invariant based inverse engineering is developed. Finally we look at non-hermitian potentials and design particular potentials that result in desirable asymmetries in the transmission and reflection of incident particles.
Adiabatic processes in quantum mechanics are very useful to prepare and manipulate quantum states but have the drawback of requiring long operation times. Hence there is a long time for the system to interact with its environment which can lead to a loss of coherence of the final state. This decoherence is problematic for implementing future quantum technologies which require the state's quantum mechanical features. “Shortcuts to Adiabaticity"(STA) provides a toolbox of methods to improve on adiabatic processes. Using these methods one can derive alternative processes which work for much shorter times with perfect fidelity. Since adiabatic processes are ubiquitous in atomic, molecular and optical physics, there is a broad scope of application for STA. In this thesis, STA (especially those using Lewis-Riesenfeld invariants) are applied to a variety of quantum systems for the purpose of quantum state transfer. In particular I show that STA control schemes in two- and three-level systems can be optimised to be more stable against unwanted uncontrollable transitions than adiabatic methods with the same operation time. I also show that STA methods can be applied in a triple well ring system with complex tunnelling, in optical lattices for the purposes of generating a higher orbital state of neutral atoms and in Penning traps to quickly compress or expand the trapped ion wavefunction. Finally I also investigate the effect of classical Poisson white noise on adiabatic processes.
Fast and robust quantum control protocols are often based on an idealized approximate description of the relevant quantum system.While this may provide a performance that is close to optimal, improvements can be made by incorporating elements of the full system representation.We propose a technique for such scenarios, called enhanced shortcuts to adiabaticity (eSTA).The eSTA method works for previously intractable Hamiltonians by providing an analytical correction to existing STA protocols.This correction can be easily calculated, and the resulting protocols are outside the class of STA schemes.We demonstrate the effectiveness of the method for three distinct cases: manipulation of an internal atomic state beyond the rotating-wave approximation, transport of a neutral atom in an optical Gaussian trap, and transport of two trapped ions in an anharmonic trap.
Quantum adiabatic processes—that keep constant the populations in the instantaneous eigenbasis of a time-dependent Hamiltonian—are very useful to prepare and manipulate states, but take typically a long time. This is often problematic because decoherence and noise may spoil the desired final state, or because some applications require many repetitions. "Shortcuts to adiabaticity" are alternative fast processes which reproduce the same final populations, or even the same final state, as the adiabatic process in a finite, shorter time. Since adiabatic processes are ubiquitous, the shortcuts span a broad range of applications in atomic, molecular, and optical physics, such as fast transport of ions or neutral atoms, internal population control, and state preparation (for nuclear magnetic resonance or quantum information), cold atom expansions and other manipulations, cooling cycles, wavepacket splitting, and many-body state engineering or correlations microscopy. Shortcuts are also relevant to clarify fundamental questions such as a precise quantification of the third principle of thermodynamics and quantum speed limits. We review different theoretical techniques proposed to engineer the shortcuts, the experimental results, and the prospects.
By definition, quantum adiabatic process means a slow process which allows the state to follow the instantaneous eigenstates of time-dependent Hamiltonian. For some reasons, for example, to avoid the decoherence effects, or to implement large-scale quantum information processing, we may want to speed up the adiabatic process, that is, to achieve the adiabatic-like control but in very short time. In this talk, we present new methods to speeded-up expansion and transport of cold atoms in a harmonic trap. Such shortcuts to adiabaticity provide the fast expansion or transport, in which the final atomic state is the same as in the adiabatic process, but in arbitrarily short time, keeping the same populations of vibrational levels in the initial and final trap. These methods can also be generalized to Bose-Einstein Condensates. Moreover, we present shortcuts to adiabatic passage from one internal atomic state to another in twoor three-level atoms. In detail, we can apply Berry’s transitionless quantum driving method and invariant-based inverse engineering method to accelerate the Rapid Adiabatic Passage (RAP) and Stimulated Raman Adiabatic Passage (STIRAP) in twoand three-level atomic systems, respectively. We also examine and compare the stability of different schemes concerning different types of noise and system errors. Finally, we show that the technique of shortcuts to adiabaticity in two-level system can be applied in fast and robust spin flip in a quantum dot, to avoid the decoherent effects.
Shortcuts to adiabaticity (STA) are a collection of quantum control techniques that achieve high fidelity outside of the adiabatic regime. Recently an extension to shortcuts to adiabaticity was proposed by the authors [Whitty, Kiely, and Ruschhaupt, Phys. Rev. Research 2, 023360 (2020)]. This method, enhanced shortcuts to adiabaticity (eSTA), provides an extension to the original STA control functions and allows effective control of systems not amenable to STA methods. It is conjectured that eSTA schemes also enjoy an improved stability over their STA counterparts. We provide numerical evidence of this claim by applying eSTA to fast atomic transport using an optical lattice and evaluating appropriate stability measures. We show that the eSTA schemes not only produce higher fidelities but also remain more stable against errors than the original STA schemes.
Quantum waveguides are one of the key components in the developement of quantum technologies that experienced a new surge in popularity in recent years. In quantum computers, quantum particles have to be moved between different sites on a quantum chip through waveguides. The progressive miniaturization of quantum chips requires the waveguides to follow certain paths and so they need to be bent in order to be accomodated onto the chip. If the bending is too abrupt, instabilities are introduced in the system, possibly causing reflection and consequently data loss. This difficulty is usually overcome by adopting the adiabatic approach: the parameter representing the bending needs to vary gently along the waveguide, to prevent disruptive effects. This method, however, cannot be applied in many settings, in particular the ones that need a high degree of compactness. Thus, a new approach that would take into account all the different requirements is needed. ``Shortcuts to Adiabaticity" (STA) offers the right platform to improve on adiabatic processes and in this thesis we will apply a protocol based on STA to maximize particle transmission fidelity in geometries where the adiabatic approach cannot be employed.