量子计算外文翻译中英文2019

量子计算外文翻译中英文2019

量子计算中英文2019

英文

FROM BITS TO QUBITS, FROM COMPUTING TO QUANTUM

COMPUTING: AN EVOLUTION ON THE VERGE OF A REVOLUTION

IN THE COMPUTING

LANDSCAPE

Pi rjan Alexandru; Petro?anu Dana-Mihaela.

ABSTRACT

The "Quantum Computing" concept has evolved to a new

paradigm in the computing landscape, having the potential to

strongly influence the field of computer science and all the fields

that make u of information technology. In this paper, we focus

first on analysing the special properties of the quantum realm, as

a proper hardware implementation of a quantum computing

system must take into account the properties. Afterwards, we

have analyzed the main hardware components required by a

quantum computer, its hardware structure, the most popular

technologies for implementing quantum computers, like the

trapped ion technology, the one bad on superconducting

circuits, as well as other emerging technologies. Our study offers

important details that should be taken into account in order to

complement successfully the classical computer world of bits

with the enticing one of qubits.

KEYWORDS: Quantum Computing, Qubits, Trapped Ion

Technology, Superconducting Quantum Circuits, Superposition,

Entanglement, Wave-Particle Duality, Quantum Tunnelling

1. INTRODUCTION

The "Quantum Computing" concept has its roots in the

"Quantum Mechanics" physics subdomain that specifies the way

how incredibly small particles, up to the subatomic level, behave.

Starting from this concept, the Quantum Computing has evolved

to a new paradigm in the computing landscape. Initially, the

concept was put forward in the 1980s as a mean for enhancing

the computing capability required to

model the way in which quantum physical systems act.

Afterwards, in the next decade, the concept has drawn an

incread level of interest due to the Shor's algorithm, which, if it

had been put into practice using a quantum computing machine,

it would have risked decrypting classified data due to the

exponential computational speedup potential offered by

quantumcomputing [1].

However, as the development of the quantum computing

machines was infeasible at the time, the whole concept was only

of theoretical value. Nowadays, what was once thought to be

solely a theoretical concept, evolved to become a reality in which

quantum information bits (entitled "qubits") can be stored and

manipulated. Both governmental and private companies alike

have an incread interest in leveraging the advantages offered

by the huge computational speedup potential provided by the

quantum computing techniques in contrast to traditional ones

[2].

One of the aspects that make the development of quantum

computers attractive consists in the fact that the shrinkage of

silicon transistors at the nanometer scale that has been taking

place for more than 50 years according to Moore's law begins to

draw to a halt, therefore arising the need for an alternate solution

[3].

Nevertheless, the most important factor that accounts for

boosting the interest in quantum computing is reprented by

the huge computational power offered by the systems and the

fact that their development from both hardware and software

perspectives has become a reality. Quantum computing

managed to surpass the computability thesis of ChurchTuring,

which states that for any computing device, its power

computation could increa only in a polynomial manner when

compared to a "standard" computer, entitled the Turing machine

[4].

During the time, hardware companies have designed and

launched "classical" computing machines who processing

performance has been improving over the time using two main

approaches: firstly, the operations have been accelerated

through an incread processing clock frequency and condly,

through an increa in the number of operations performed

during each processing clock's cycle [5].

Although the computing processing power has incread

substantially after having applied the above-mentioned

approaches, the overall gain has remained in

accordance with the thesis of Church-Turing. Afterwards, in

1993, Bernstein and Vazirani have published in [6] a theoretical

analysis stating that the extended Church-Turing thesis can be

surpasd by means of quantum computing. In the following year,

Peter Shor has proved in his paper that by means of

quantumcomputing the factorization of a large number can be

achieved with an exponentially computing speedup when

compared to a classical computing machine [7-9]. Astonishing as

the theoretical framework was, a viable hardware

implementation was still lacking at the time.

The first steps for solving this issue have been made in 1995,

when scientists have laid the foundations for a technology bad

on a trapped ion system [10] and afterwards, in 1999, for a

technology employing superconducting circuits [11]. Bad on

the advancement of technology, over the last decades,

rearchers have obtained huge progress in this field, therefore

becoming able to build and employ the first quantum computing

systems.

While in the ca of a classical computing machine the data

is stored and procesd as bits (having the values 0 or 1), in the

ca of a quantum computingmachine, the basic unit of quantum

information under which the data is stored and procesd is

reprented by the quantum bits, or qubits that can have besides

the values of 0 and 1, a combination of both the values in the

same time, reprenting a "superposition" of them [12].

At a certain moment in time, the binary values of the n bits

corresponding to a classical computer define a certain state for

it, while in the ca of a quantumcomputer, at a certain moment

in time, a number of n qubits have the possibility to define all the

classical computer's states, therefore covering an exponential

incread computational volume. Nevertheless, in order to

achieve this, the qubits must be quantum entangled, a non-local

property that makes it possible for veral qubits to be correlated

at a higher level than it was previously possible in classical

computing. In this purpo, in order to be able to entangle two

or veral qubits, a specific controlled environment and special

conditions must be met [13].

During the last three decades, a lot of studies have been

aiming to advance the

state of knowledge in order to attain the special conditions

required to build functional quantum computing systems.

Nowadays, besides the most popular technologies employed in

the development of quantum computing systems, namely the

ones bad on trapped ion systems and superconducting circuits,

a wide range of other alternative approaches are being

extensively tested in complex rearch projects in order to

successfully implement qubits and achieve quantum computing

[14].

One must take into account the fact that along with the new

hardware architectures and implementations of quantum

computing systems, new challenges ari from the fact that this

new computing landscape necessitates new operations,

computing algorithms, specialized software, all of the being

different than the ones ud in the ca of classical computers.

A proper hardware implementation of a quantum computing

system must take into account the special properties of the

quantum realm. Therefore, this paper focus first on analyzing

the characteristics and afterwards on prenting the main

hardware components required by a quantum computer, its

hardware structure, the most popular technologies for

implementing quantum computers, like the trapped ion

technology, the one bad on superconducting circuits, as well

as other emerging technologies. Our developed rearch offers

important details that should be taken into account in order to

complement successfully the classical computer world of bits

with the enticing one of qubits.

L PROPERTIES OF THE QUANTUM REALM

The huge processing power of quantum computers results

from the capacity of quantum bits to take all the binary values

simultaneously but harnessing this vast amount of

computational potential is a challenging task due to the special

properties of the quantum realm. While some of the special

properties bring considerable benefits towards quantum

computing, there are others that can hinder the whole process.

One of the most accurate and extensively tested theory that

comprehensibly describes our physical world is quantum

mechanics. While this theory offers intuitive explanations for

large-scale objects, while still very accurate also at the subatomic

level, the explanations might em counterintuitive at the

first sight. At the quantum level, an object does not have a certain

predefined state, the object can behave like a particle when a

measurement is performed upon it and like a wave if left

unmeasured, this reprenting a special quantum property

entitled wave-particle duality [15].

The global state of a quantum system is determined by the

interference of the multitude of states that the objects can

simultaneously have at a quantum level, the state being

mathematically described through a wave function. Actually, the

system's state is often described by the sum of the different

possible states of its components, multiplied by a coefficient

consisting in a complex number, reprenting, for each state, its

relative weight [16, 17]. For such a complex coefficient, by taking

into consideration its trigonometric (polar) form, one can write it

under the form Aew = A(cos6 + i sind), where A > 0 reprents

the module of this complex number and is denoted as the

"amplitude", while в reprents the argument of the complex

number, being denoted as "the pha shift". Therefore, the

complex coefficient is known if the two real numbers A and в are

known.

All the constitutive components of a quantum system have

wave-like properties, therefore being considered "coherent". In

the ca of coherence, the different states of the quantum

components interact between them, either in a constructive

manner or in a destructive one [1]. If a quantum system is

measured at a certain moment, the system expos only a single

component, the probability of this event being equal to the

squared absolute value of the corresponding coefficient,

multiplied by a constant. If the quantum system is measured,

from that moment on it will behave like a classical system,

therefore leading to a disruption of its quantum state. This

phenomenon caus a loss of information, as the wave function

is collapd, and only a single state remains. As a conquence

of the measurement, the wave function associated to the

quantum obj ect corresponds only to the measured state [1, 17].

Considering a qubit, one can easily demonstrate that its

quantum state could be reprented by a linear superposition of

two vectors, in a space endowed with a scalar product having the

dimension 2. The orthonormal basis in this space consists of the

vectors denoted as |0 >= [Jj and |1 >= [°j. If one considers

two qubits, they could be reprented as a linear combination of

the 22 elements of the ba, namely the ones denoted as ....

Generally, in the ca of n qubits, they could be reprented by a

superposition state vector in a space having the dimension 2n [2].

Another special property of the quantum realm consists in

the entanglement, a property that has the ability to exert a

significant influence on quantumcomputing and open up a

plethora of novel applications. The physical phenomenon of

quantum entanglement takes place when two (or more)

quantumobjects are intercorrelated and therefore the state of a

quantum object influences instantaneously the state(s) of the

other(s) entangled quantum object(s), no matter the distance(s)

between the objects [16].

Another important quantum mechanical phenomenon that

plays a very important role in quantum computing is quantum

tunneling that allows a subatomic particle to go through a

potential barrier, which otherwi would have been impossible to

achieve, if it were to obey only the physical laws of classical

mechanics. An explanation of this different behavior consists in

the fact that in quantum mechanics the matter is treated both as

waves and particles, as we have described above, when we have

prented the wave-particle duality concept [15].

The Schr?dinger equation describes the variation of the wave

function, taking into account the energy environment that acts

upon a quantum system, therefore highlighting the way in which

this quantum system evolves. In order to obtain the

mathematical description of the environment, of the energies

corresponding to all the forces acting upon the system, one us

the Hamiltonian of the quantum system. Therefore, the control

of a quantum system can be achieved by controlling its energy

environment, which can be obtained by isolating the system from

the external forces, and by subjecting the system to certain

energy fields as to induce a specific behavior. One should note

that a perfect isolation of the quantum system from the external

world cannot be achieved, therefore in practice the interactions

are minimized as much as possible. Over time, the quantum

system is continuously influenced to a small extent by the

external environment, through a process called "decoherence",

process that modifies the wave function, therefore collapsing

it to a certain degree [1].

Figure 1 depicts the main special properties of the quantum

realm, which, when precily controlled, have the ability to

influence to a large extent the performance of a quantum

computer implementation, and open up new possibilities for

innovation concerning the storing, manipulation and processing

of data.

In the following, we analyze a ries of hardware components

and existing technologies ud for developing and implementing

quantum computers.

OVERVIEW OF THE NECESSARY HARDWARE AND OF

THE EXISTING TECHNOLOGIES USED IN THE IMPLEMENTATIONS

OF QUANTUM COMPUTERS

A proper hardware architecture is vital in order to be able to

program, manipulate, retrieve qubits and overall to achieve an

appropriate and correct quantumcomputer implementation.

When implementing a quantum computer at the hardware level,

one must take into account the main hardware functions, a

proper modularization of the equipment along with both

similarities and differences between quantum and classic

computer implementations. Conventional computers are an

esntial part in the successful implementation of a quantum

computer, considering the fact that after having performed its

computation, a quantumcomputer will have to interact with

different categories of urs, to store or transmit its results using

classic computer networks. In order to be efficient, quantum

computers need to precily control the qubits, this being an

aspect that can be properly achieved by making u of classic

computing systems.

The scientific literature [1, 18, 19] identifies four abstract

layers in the conceptual modelling process of quantum

computers. The first layer is entitled the "quantum data plane"

and it is ud for storing the qubits. The cond layer, called

"control and measurement plane", performs the necessary

operations and measurement actions upon the qubits. The third

layer entitled "control processor plane" ts up the particular

order of operations that need to be performed along with the

necessary measurement actions for the algorithms, while the

fourth abstract layer, the "host processor", consists in a classical

computer that manages the interface with

the different categories of personnel, the storage of data and

its transmission over the networks.

In the following, we prent the two most popular

technologies employed in the development of quantum

computing systems, namely the ones bad on trapped ion

systems and superconducting circuits and, afterwards, other

alternative approaches that are being extensively tested in

complex rearch projects in order to successfully implement

qubits and achieve quantum computing.

By means of trapping atomic ions, bad on the theoretical

concepts prented by Cirac et al within [20], in 1995, Monroe et

al [21] revealed the first quantumlogic gate. This was the starting

point in implementing the first small scale quantum processing

units, making it possible to design and implement a rich variety

of basic quantum computing algorithms. However, the

challenges to scale up the implementations of quantum

computers bad on the trapped ion technology are enormous

becau this process implies a synergy of complex technologies

like coherent electronic controllers, lar, radio frequency,

vacuum, microwave [1, 22].

In the ca of a quantum computer bad on the trapped

atomic ions technology, the qubits are reprented by atomic

ions contained within the quantum data plane by a mechanism

that keeps them in a certain fixed location. The desired

operations and measurement actions are performed upon the

qubits using accurate lars or a source of microwave

electromagnetic radiation in order to alter the states of the

quantum objects, namely the atomic ions. In order to reduce the

velocity of the quantum objects and perform measurements

upon them, one us a lar beam, while for asssing the state

of the ions one us photon detectors [14, 23, 24]. Figure 2

depicts an implementation of the quantum trapping atomic ions

technology.

Another popular technology ud in the development and

implementation of quantum computers is bad on

superconducting quantum circuits. The quantum circuits have

the property of emitting quantized energy when expod to

temperatures of 10-3K order, being referred in the literature as

"superconducting artificial atoms" [25]. In contrast to classic

integrated circuits, the superconducting quantum circuits

incorporate a distinctive characteristic, namely a

"Jophson junction" that us wires made of

superconducting materials in order to achieve a weak connection.

The common way of implementing the junction consists in using

an insulator that expos a very thin layer and is created through

the Niemeyer-Dolan technique which is a specialized lithographic

method that us thin layers of film in order to achieve

overlapping structures having a nanometer size [26].

Superconducting quantum circuits technology pos a ries

of important advantages, offering red3uced decoherence and an

improved scale up potential, being compatible with microwaves

control circuits, operating with time scales of the nanocond

order [1]. All of the characteristics make the superconducting

quantum circuits an attractive and performant technique in

developing quantum computers. A superconducting quantum

circuit developed by D-Wave Systems Inc. is depicted in Figure 3.

In order to overcome the numerous challenges regarding the

scaling of quantum computers developed bad on trapped ion

systems and superconducting circuits, many scientists focus their

rearch activity on developing emerging technologies that

leverage different approaches for developing

quantumcomputers.

One of the alternatives that scientists investigate consists in

making u of the photons' properties, especially of the fact that

photons have a weak interaction between each other and also

with the environment. The photons have been tested in a ries

of quantum experiments and the obtained results made the

rearchers remark that the main challenge in developing

quantum computers through this approach is to obtain gates

that operate on spaces of two qubits, as at the actual moment

the photons offer very good results in terms of single qubit gates.

In order to obtain the two-qubit gates, two alternative

approaches are extensively being investigated as the have

provided the most promising results.

The first approach is bad on operations and measurements

of a single photon, therefore creating a strong interaction, uful

in implementing a probabilistic gate that operates on a space of

two qubits [1]. The cond alternative approach employs

miconductor crystals structures of small dimensions in order to

interact with the photons. The small structures can be found in

nature, ca in which they are called

"optically active defects", but can also be artificially created,

ca in which they are called "quantum dots". An important

challenge that must be overcome when analyzing quantum

computers bad on photons is their size. Until now, the

development of this type of computers has been possible only

for small dimensions, as a ries of factors limit the possibility to

increa the dimensions of photon quantum computers: the very

small wavelengths of the photons (micron-size), their very high

speed (the one of the light), the direction of their movement

being along a certain dimension of the optical chip. Therefore,

trying to significantly increa the number of qubits (reprented

by the photons) proves to be a difficult task in the ca of a

photonic device, much more difficult than in the ca of other

systems, in which the qubits are located in space. Nevertheless,

the evolution of this emerging technology promis efficient

implementations in the near future [27].

Another technology that rembles the one of "trapping

atomic ions" for obtaining qubits consists in the u and

manipulation of neutral atoms by means of microwave radiation,

lars and optics. Just like in the ca of the trapping atomic ions

technology, the "cooling" process is achieved using lar sources.

According to [1, 28], in 2018 there were implemented successfully

quantum systems having 50 qubits that had a reduced space

between them. By means of altering the space between the

qubits, the quantum systems proved to be a successful analog

implementation of quantum computers. In what concerns the

error rates, according to [29], in 2018 there have been registered

values as low as 3% within two-qubit quantum systems that

managed to isolate properly the operations performed by nearby

qubits. Since there are many similarities between the two

technologies, the scaling up process faces a lot of the problems

of the "trapping atomic ions" technology. However, the u of the

neutral atoms technology offers the possibility of creating

multidimensional arrays.

A classification of miconductor qubits is made according

to the method ud to manipulate the qubits that can be

achieved either by photon manipulation or by using electrical

signals. Quantum dots are ud in the ca of miconductor

qubits that are gated by optical means in order to assure a strong

coupling of the photons while in the ca of miconductor

qubits manipulated via electrical signals, voltages are ud

upon lithographically metal gates for manipulating the

qubits [1]. This quantum technology, although being less popular

than other alternatives, rembles the existing classical electronic

circuits, therefore one might argue that it has a better chance in

attracting considerable investments that eventually will help

speed up the scaling up process of quantum computers

implementation.

In order to scale up qubits that are optically gated, one needs

a high degree of consistency and has to process every qubit

parately at the optical level. In [30], Pla et al. state that even if

the qubits that are gated electrically can be very den, the

material related problems pod not long-ago rious quality

problems up to single qubits gates level. Although the high

density provided by this type of quantum technology creates

opportunities for integrating a lot of qubits on a single processor,

complex problems ari when one has to manipulate this kind of

qubits becau the wiring will have to assure an isolation of the

control signals as to avoid interference and crosstalk.

Another ongoing approach in developing quantum

computers consists in using topological qubits within which the

operations to be performed upon are safeguarded due to a

microscopically incorporated topological symmetry that allows

the qubit to correct the errors that may ari during the

computing process [1]. If in the future this approach materializes,

the computational cost associated with correcting the quantum

errors will diminish considerably or even be eliminated altogether.

Although this type of technology is still in its early stages, if

someday one is able to implement it and prove its technical

feasibility, the topological quantum computers will become an

important part of the quantum computing landscape.

4. CONCLUSIONS

Quantum computing reprents a field in a continuous

evolution and development, a huge challenge in front of

rearchers and developers, having the potential to influence and

revolutionize the development of a wide range of domains like

the computing theory, information technology, communications

and, in a general framework, regarding from the time perspective,

even the evolution and progress of society itlf. Therefore, each

step of the quantum computers' evolution has the

potential to become of paramount importance for the

humanity: from bits to qubits, from computing to quantum

computing, an evolution on the verge of a revolution in the

computing landscape.

中文

从比特到量子比特，从计算到量子计算：计算机革命的演变

抽象

“量子计算”的概念已发展成为计算领域的一个新范例，具有极

大地影响计算机科学领域和所有利用信息技术的领域的潜力。在本文

中，我们首先着重分析量子域的特殊属性，因为量子计算系统的正确

硬件实现必须考虑这些属性。之后，我们分析了量子计算机所需的主

要硬件组件，其硬件结构，用于实现量子计算机的最流行技术，例如

俘获离子技术，基于超导电路的技术以及其他新兴技术。我们的研究

提供了重要的细节，应该用诱人的量子比特来成功地补充经典的计算

机世界，应该考虑这些重要细节。

关键字：量子计算，量子位，俘获离子技术，超导量子电路，叠

加，纠缠，波粒对偶，量子隧穿

1.引言

“量子计算”概念起源于“量子力学”物理学子域，该子域指定

了直到亚原子级的不可思议的小粒子的行为方式。从这一概念开始，

量子计算已发展成为计算领域的新范例。最初，该概念是在80年代提

出的，目的是增强对量子物理系统的行为建模所需的计算能力。此后，

在接下来的十年中，由于Shor算法的出现，该概念引起了越来越多的

关注，如果使用量子计算机将其付诸实践，由于指数计算速度的加快，

它将有解密机密数据的风险。量子计算提供的潜力。

但是，由于当时量子计算机的发展还不可行，因此整个概念仅具

有理论价值。如今，曾经被认为仅仅是一个理论概念的事物逐渐发展

成为一种现实，可以存储和操作量子信息位（称为“量子位”）。与

每个处理时钟周期[5]中执行的操作数。

尽管在应用了上述方法之后，计算处理能力已大大提高，但是根

据Church-Turing的研究文献，总体收益仍然保持不变。之后，在

1993年，伯恩斯坦（Bernstein）和瓦兹拉尼（Vazirani）在理论研究

中发表了文章，指出通过量子计算可以超越扩展的丘奇－图灵论点。

在接下来的一年中，彼得·索尔（Peter Shor）在他的论文中证明，与

经典计算机相比，通过量子计算，可以以指数级的计算速度实现大量

分解。尽管理论框架令人惊讶，但当时仍缺乏可行的硬件实现。

解决这个问题的第一步是在1995年，当时科学家为基于离子束缚

系统的技术奠定了基础，随后在1999年为采用超导电路的技术奠定了

基础。随着技术的进步，在过去的几十年中，研究人员在该领域取得

了巨大的进步，因此能够构建和使用第一个量子计算系统。

在传统计算机的情况下，数据以位（具有值0或1）进行存储和处

理，在量子计算机的情况下，表示数据在其下存储和处理的基本信息

单位通过量子比特或除0和1之外还可以具有的量子比特，同时将这

两个值组合在一起，表示它们的“叠加”。

在某个时刻，对应于经典计算机的n位二进制值为其定义了某种

状态，而在量子计算机的情况下，在某一时刻，n个量子位有可能定义

所有经典计算机的状态，因此涵盖了呈指数增长的计算量。尽管如此，

为了实现这一点，量子位必须被量子纠缠，这是一种非局部性质，这

使得几个量子位可以比以前在传统计算中更高的水平相关。为此目的，

为了能够纠缠两个或几个量子比特，必须满足特定