How to create indexes using Hibernate for PostgreSQL

I am working on a Spring-MVC application in which I am using Hibernate as the ORM tool with PostgreSQL. For some of the entities in the project Model, I would like to create Indexes for faster lookup. As I read, I found out it is possible to create indexes using Hibernate. Unfortunately, I am not having much luck. I only tried to create it on one Model class, but when I check in PGAdmin, I cannot see any index for that table.

When I try giving the @Index parameter to the @Table annotation, I get error. Can anyone tell me how I can annotate columns and entire table for auto-indexing by Hibernate. Thanks a lot.

Online User model : // This class I just used for testing

import org.hibernate.search.annotations.Indexed;

import javax.persistence.*;
@Entity
@Table(name="onlineusers" )
@Indexed(index = "onlineuserindex")
public class OnlineUsers {

  @Id
    @Column(name="onlineuserid")
    @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "online_gen")
    @SequenceGenerator(name = "online_gen",sequenceName = "online_seq")
    private int onlineUserId;


    @Column(name = "onlineusername")
    private String personName;
}

Please note, when I try something like this below :

@Indexed(index = "usernameindex");
@Column(name="username");
private String userName;

I get an error, @Indexed not applicatble to a field.

POM.xml :

 <properties>
        <java-version>1.8</java-version>
        <org.springframework-version>4.0.6.RELEASE </org.springframework-version>
        <org.aspectj-version>1.7.4</org.aspectj-version>
        <org.slf4j-version>1.7.5</org.slf4j-version>
        <hibernate.version>4.3.9.Final</hibernate.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    </properties>

  <!-- Hibernate search dependencies -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-search-orm</artifactId>
            <version>5.2.0.Final</version>
        </dependency>

    <!--    <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-annotations</artifactId>
            <version>3.5.6-Final</version>
        </dependency>
-->

Kindly let me know what I am doing wrong. Thanks a lot. :-)